<PAGE>

                                                                 EXHIBIT 10.6(a)


          This Warrant and the securities issuable upon exercise hereof not been
          registered under the Securities Act of 1933, as amended (the
          "Securities Act") or under any applicable state securities law, and in
          the absence of such registration may not be sold or transferred unless
          the issuer of this Warrant has received an opinion of its counsel, or
          of counsel reasonably satisfactory to it, that the proposed sale or
          transfer will not violate the registration requirements of the
          Securities Act or any applicable state securities law.


                           EINSTEIN/NOAH BAGEL CORP.

                        WARRANT CERTIFICATE TO PURCHASE
                             SHARES OF COMMON STOCK
                             ----------------------



Date of Issuance:  November 21, 1997                        Certificate W-BOA-1

     FOR VALUE RECEIVED, Einstein/Noah Bagel Corp., a Delaware corporation (the
"Company"), hereby grants to Bank of America National Trust and Savings
Association (the "Registered Holder") the right to purchase from the Company
20,000 shares of the Company's Common Stock, $.01 par value, at a price per
share of $9.47 (as adjusted from time to time in accordance herewith, the
"Exercise Price").

     This Warrant is subject to the following provisions:

     Section 1.  Exercise of Warrant.
                 -------------------

     1A.  Exercise Period.  The Registered Holder may exercise, in whole or in
part, the purchase rights represented by this Warrant at any time and from time
to time during the period commencing on Date of Issuance of this Warrant set
forth above and ending on the third annual anniversary of the Date of Issuance
(the "Exercise Period").

     1B.  Exercise Procedure.

          (i) This Warrant shall be deemed to have been exercised when the
Company has received all of the following items (the "Exercise Time"):

               (a) a completed Exercise Agreement, as described in paragraph 1C
     below, executed by the person exercising all or part of the purchase rights
     represented by this Warrant (the "Purchaser");

               (b)  this Warrant;
<PAGE>

               (c) cash (payable by wire transfer of same day funds or a
     certified or bank cashier's check) in an amount equal to the product of the
     Exercise Price multiplied by the number of shares of Company Common Stock
     being purchased upon such exercise (the "Aggregate Exercise Price") or, at
     the option of the Registered Holder, the Registered Holder may elect to
     receive shares of Company Common Stock equal to the value of this Warrant
     by surrender of this Warrant to the Company, in which event the Company
     shall issue to the Purchaser a number of shares of Company Common Stock
     computed using the following formula:

                   x = y(a-b)
                       ------
                         a

         where:    x = The number of shares of Company Common Stock to be
                       issued to the  Purchaser

                   y = The number of shares of Company Common Stock purchasable
                       under this Warrant (at the date of such calculation).

                   a = The "Fair Market Value'' of one share of Company Common
                       Stock (at the date of such calculated

                   b = The Exercise Price (as adjusted to the date of such
                       calculation).

     As used in this Section I.B., the term "Fair Market Value" of a share of
     Company Common Stock means the average of the closing prices of sales of
     the Company's Common Stock on all securities exchanges or automated
     quotation system on which the Company's Common Stock may at the time be
     listed or included, or, if there has been no sales on any such exchange or
     reported on such quotation system on any day, the average of the highest
     bid and lowest asked prices on all such exchanges as reported at the end of
     such day, or, if on any day the Company's Common Stock is not so listed or
     included in any such quotation system, the average of the highest bid and
     lowest asked prices on such day in the domestic over-the-counter market as
     reported by the National Quotation Bureau, Incorporated, or any similar
     successor organization, in each such case averaged over a period of 21 days
     consisting of the third day immediately prior to the day as of which "Fair
     Market Value" is being determined and the 20 consecutive business days
     prior to such day.

          (ii) Certificates for shares of Common Stock, if any, purchased upon
exercise of this Warrant shall be delivered by the Company to the Purchaser
within five business days after the Exercise Time.  Unless this Warrant has
expired or all of the purchase rights represented hereby have been exercised,
the Company shall prepare a new Warrant, substantially identical hereto,
representing the rights formerly represented by this Warrant which have not
expired or been exercised and shall, as soon as reasonably practicable, deliver
such new Warrant to the person designated for delivery in the Exercise
Agreement.

                                       2
<PAGE>

          (iii)  The shares of Common Stock issuable upon the exercise of this
Warrant shall be deemed to have been issued to the Purchaser at the Exercise
Time, and the Purchaser shall be deemed for all purposes to have become the
record holder of such shares of Common Stock at the Exercise Time irrespective
of the date of delivery of certificates for shares of Common Stock.

          (iv) The issuance of certificates for shares of Common Stock, if any,
upon exercise of this Warrant shall be made without charge to the Registered
Holder or the Purchaser for any issuance tax in respect thereof or other cost
incurred by the Company in connection with such exercise and the related
issuance of shares of Common Stock (other than the Aggregate Exercise Price).
Each share of Common Stock issuable upon exercise of this Warrant shall, when
issued, be duly and validly issued and free from all taxes, liens, encumbrances,
adverse claims and charges.

          (v) The Company shall reasonably assist and cooperate with the
Registered Holder or Purchaser required to make any governmental filings or
obtain any governmental approvals prior to or in connection with any exercise of
this Warrant (including, without limitation, making any reasonable filings
required to be made by the Company), provided, however, that the Company will
not be required to (A) qualify generally to do business in any jurisdiction
where it would not otherwise be required to qualify but for this subparagraph
(v), (B) subject itself to taxation in any such jurisdiction, or (C) consent to
general service of process in any such jurisdiction.

          (vi) The Company shall at all times reserve and keep available out of
its authorized but unissued Common Stock solely for the purpose of issuance upon
the exercise of this Warrant the maximum number of shares issuable upon the
exercise of this Warrant.  All shares which are so issuable shall, when issued
in accordance herewith upon the payment of the Exercise Price, be duly and
validly issued, fully paid and nonassessable and free from all taxes, liens,
encumbrances, adverse claims and charges.  The Company shall take all such
actions as may be reasonably necessary to assure that all such shares of Common
Stock may be so issued without violation of any applicable law or governmental
regulation or any requirements of any domestic securities exchange upon which
shares of Common Stock of the Company or their equivalents may be listed (except
for official notice of issuance which shall be immediately delivered by the
Company upon such issuance).

          (vii)  Notwithstanding any other provision hereof, if an exercise of
any portion of this Warrant is to be made in connection with a registered public
offering of the Company or any event described in Section 2B hereof, the
exercise of any portion of this Warrant may, at the election of the Registered
Holder hereof, be conditioned upon the consummation of the public offering or
the event described in Section 2B, in which case such exercise shall not be
deemed to be effective until the consummation of such transaction.

                                       3
<PAGE>

          (viii)  Unless the shares of Common Stock to be issued upon exercise
of this Warrant have been registered under the Securities Act of 1933, as
amended, the certificates for such shares shall contain the following legend:

     "The securities represented by this certificate have not been registered
under the Securities Act of 1933, as amended ("Securities Act"), or under any
applicable state securities law, and may not be resold or transferred unless
registered under the Securities Act or unless the Company has received an
opinion of its counsel, or of counsel reasonably satisfactory to it, that the
proposed transfer will not violate the registration requirements of the
Securities Act or any applicable state securities law."

     1C.  Exercise Agreement.  Upon any exercise of this Warrant, the Exercise
Agreement shall be substantially in the form set forth in Exhibit IA or IB
hereto, except that if the shares of Common Stock are not to be issued in the
name of the person in whose name this Warrant is registered, the Exercise
Agreement shall also state the name of the person to whom the shares of Common
Stock are to be issued. Such Exercise Agreement shall be dated the actual date
of execution thereof.

     Section 2.  Adjustment of Exercise Price and Number of Shares.  The
Exercise Price and the number of shares of Common Stock (or other securities)
obtainable upon exercise of this Warrant shall be subject to adjustment from
time to time as provided in this Section 2.

     2A.  Subdivision or Combination of Shares of Common Stock.  If the Company
at any time subdivides (by any split, dividend, recapitalization or otherwise)
one or more classes of its outstanding shares of Common Stock into a greater
number of shares, the Exercise Price in effect immediately prior to such
subdivision shall be proportionately reduced and the number of shares of Common
Stock obtainable upon exercise of this Warrant shall be proportionately
increased.  If the Company at any time combines (by reverse split or otherwise)
one or more classes of its outstanding shares of Common Stock into a smaller
number of shares, the Exercise Price in effect immediately prior to such
combination shall be proportionately increased and the number of shares of
Common Stock obtainable upon exercise of this Warrant shall be proportionately
decreased.

     2B.  Options and Convertible Securities.  If the Company at any time shall
pay a dividend or make a distribution with respect to the Common Stock payable
in Options (as hereinafter defined) or Convertible Securities (as hereinafter
defined), the Exercise Price shall be adjusted, from and after the date of
determination of shareholders entitled to receive such dividend or distribution,
to that price determined by multiplying the Exercise Price in effect immediately
prior to such date of determination by a fraction (i) the numerator of which
shall be the total number of shares of Common Stock outstanding immediately
prior to such dividend or distribution, and (ii) the denominator of which shall
be the total number of shares of Common Stock outstanding immediately after such
dividend or distribution (including shares of Common Stock issuable upon
exercise, conversion or exchange of any Option or Convertible Securities issued
as such dividend or distribution).  Upon any adjustment to the Exercise Price
pursuant to this Section 2B, the number of shares of Company Common Stock
issuable upon exercise of this

                                       4
<PAGE>

Warrant shall be adjusted to the product obtained by multiplying the number of
shares of Company Common Stock issuable immediately prior to such adjustment in
the Exercise Price by a fraction (a) the numerator of which shall be the
Exercise Price immediately prior to such adjustment and (b) the denominator of
which shall be the Exercise Price immediately after such adjustment. As used in
this Section 2B, the term "Options" means rights, options or warrants to
subscribe for, purchase or otherwise acquire shares of Common Stock or
Convertible Securities. As used in this Section 2B, the term "Convertible
Securities" means any evidence of indebtedness or shares of stock or other
securities directly or indirectly convertible into or exchangeable for shares of
Common Stock. Any adjustment under this Section 2B shall become effective on the
record date.

     2C.  Other Securities.  If the Company makes or fixes a record date for the
determination of holders of Common Stock entitled to receive a dividend or other
distribution payable in securities of the Company other than shares of Common
Stock, then, and in each such event, provision shall be made so that the
Registered Holder shall receive, upon exercise hereof, in addition to the number
of shares of Company Common Stock receivable upon exercise of this Warrant, the
amount of securities of the Company which the Registered Holder would have
received had this Warrant been exercised for such shares of Company Common Stock
on the date of such event and had the Registered Holder thereafter, during the
period from the date of such event to and including the date of exercise,
retained such securities receivable by the Registered Holder as aforesaid during
such period, subject to all other adjustments called for during such period
under this Section 2.

     2D.  Reorganization, Reclassification, Consolidation or Merger.  The shares
of Common Stock issuable upon exercise of this Warrant shall be adjusted as
follows:  (a) in the event of any merger, consolidation, reclassification, sale
of all or substantially all of the Company's assets, or reorganization of the
Company with any other person or persons, there shall be substituted, on an
equitable basis, for each such share of Common Stock the number and kind of
shares of stock or other securities to which the holders of each share of Common
Stock of the Company will be entitled pursuant to the transaction and the
Company shall not consummate any such transaction unless provision has been made
for issuance of such stock or other securities upon exercise of this Warrant;
and (b) in the event of any other substantially similar change in the
capitalization of the Company (other than cash dividends in the ordinary course
of business), an equitable adjustment shall be provided in the number of shares
of Common Stock.  In the event of any such adjustment the purchase price per
share shall be proportionately adjusted.

     2E.  Notice of Adjustment.  Promptly upon any adjustment of the Exercise
Price or the number of shares of Common Stock issuable upon exercise of this
Warrant, the Company shall give written notice thereof to the Registered Holder,
setting forth in reasonable detail and certifying the calculation of such
adjustment.

     Section 3.  No Voting Rights; Limitations of Liability.  This Warrant shall
not entitle the holder hereof to any voting rights or other rights as a holder
of  shares of Common Stock in the Company.  No provision hereof, in the absence
of affirmative action by the Registered Holder to purchase shares of Common
Stock, and no enumeration herein of the rights or privileges of the Registered

                                       5
<PAGE>

Holder shall give rise to any liability of such holder for the Exercise Price of
Shares of Common Stock acquirable by exercise hereof or as a holder of shares of
Common Stock in the Company.

     Section 4.  Transferability.  Except as provided in this Section 4, this
Warrant and all rights hereunder are not transferable without the prior written
consent of the Company in its sole discretion. The restrictions on transfer of
this Warrant shall continue during the entire term of this Warrant.  Subject to
the transfer conditions referred to in the legend endorsed hereon and the
provisions of this Section 4, this Warrant and all rights hereunder are
transferable, in whole or in part, upon surrender of this Warrant with properly
executed Assignment (in the form of EXHIBIT II hereto) at the principal office
of the Company; provided that no transfer of all or any part of this Warrant may
be made if such transfer would cause the aggregate number of holders of warrants
derived from this Warrant to be held by more than seven persons; and provided,
further, each such transferee must be an "accredited investor" within the
meaning of Regulation D of the Securities Act. The Company shall not impose any
fee or charge for such transfer.  No such transferee receiving this Warrant or
any warrant derived herefrom may transfer such warrant or any of its rights
without the prior written consent of the Company in its sole discretion.
Notwithstanding any provision of this Section 4, the Registered Holder and any
transferee receiving this Warrant may transfer this Warrant to any Affiliate of
the Registered Holder or such transferee, so long as the issuer of this Warrant
has received an opinion of its counsel, or of counsel reasonably satisfactory to
it, that the proposed sale or transfer will not violate the registration
requirements of the Securities Act or any applicable state securities law.  As
used in this Section 4, the term "Affiliate" means with respect to any
Registered Holder or transferee, any other person directly or indirectly
controlling or controlled by or under direct or indirect control with such
Registered Holder or transferee.  Shares issued pursuant to this Warrant or any
warrant derived herefrom shall be subject to the same transfer restrictions as
set forth herein for this Warrant, provided that the restrictions on
transferability of shares issuable upon exercise of any such warrant shall only
apply until (i) such securities shall have been registered under the Securities
Act of 1933, as amended (the "Securities Act") and disposed of in accordance
with a registration statement covering such securities, or (ii) such time as, in
the reasonable opinion of counsel for the Company, or upon the written opinion
of counsel for the holder thereof reasonably acceptable to the Company, such
restrictions are not required in order to comply with the Securities Act.
Whenever such restrictions shall terminate as to any shares issued upon exercise
of any such warrant, the holder thereof shall be entitled to receive from the
Company, without expense, new certificates of like tenor not bearing the
restrictive legends required hereby.

     Section 5.  Warrant Exchangeable for Different Denominations.  This Warrant
is exchangeable, upon the surrender hereof by the Registered Holder at the
principal office of the Company, for new Warrants of like tenor representing in
the aggregate the purchase rights hereunder, and each of such new Warrants shall
represent such portion of such rights as is designated by the Registered Holder
at the time of such surrender.  The date the Company initially issues this
Warrant shall be deemed to be the "Date of Issuance" hereof regardless of the
number of times new certificates representing the unexpired and unexercised
rights formerly

                                       6
<PAGE>

represented by this Warrant shall be issued. All Warrants representing portions
of the rights hereunder are referred to herein as the "Warrants."

     Section 6.  Replacement.  Upon receipt of evidence reasonably satisfactory
to the Company of the ownership and the loss, theft, destruction or mutilation
of any certificate evidencing this Warrant, and in the case of any such loss,
theft or destruction, upon receipt of indemnity reasonably satisfactory to the
Company, or, in the case of any such mutilation upon surrender of such
certificate, the Company shall (at its expense) execute and deliver in lieu of
such certificate a new certificate of like kind representing the same rights
represented by such lost, stolen, destroyed or mutilated certificate and dated
the date of such lost, stolen, destroyed or mutilated certificate.

     Section 7.  Notices.  Except as otherwise expressly provided herein, all
notices referred to in this Warrant shall be in writing and shall be delivered
personally, sent by reputable overnight courier service (charges prepaid), sent
by fax or sent by registered or certified mail, return receipt requested,
postage prepaid, as follows:  (i) if given to the Company, at its principal
executive offices and (ii) if given to the Registered Holder of this Warrant, at
such holder's address as it appears in the records of the Company.  Each such
notice shall be deemed to have been given upon the earlier of the receipt of
such notice by the intended recipient thereof, two business days after it is
sent by reliable overnight courier or sent by fax, or five business days after
it is mailed by registered or certified mail, return receipt requested.

     Section 8.  Amendment and Waiver.  Except as otherwise provided herein, the
provisions of the Warrants may be amended and the Company may take any action
herein prohibited, or omit to perform any act herein required to be performed by
it, only if the Company has obtained the written consent of the Registered
Holders of Warrants representing a majority of the shares of Common Stock
obtainable upon exercise of the Warrants; provided that no such action may
change the Exercise Price of the Warrants or the number or class of shares of
Common Stock obtainable upon exercise of each Warrant without the written
consent of all of the Registered Holders of Warrants.

     Section 9.  Descriptive Headings; Governing Law.  The descriptive headings
of the several Sections and paragraphs of this Warrant are inserted for
convenience only and do not constitute a part of this Warrant.  The laws of the
State of Delaware shall govern all issues concerning the relative rights of the
Company and the Registered Holder of this Warrant.

     Section 10.  Fractional Shares.  No fractional shares shall be issued in
connection with any exercise of this Warrant, but in lieu of such fractional
shares the Company shall make a cash payment therefor upon the basis of the
Exercise Price then in effect.

                                       7
<PAGE>

     IN WITNESS WHEREOF, the Company has caused this Warrant to be signed and
attested by its duly authorized officers under its corporate seal and to be
dated the Date of Issuance hereof.

                                EINSTEIN/NOAH BAGEL CORP.

                                By:   /s/ PAUL A. STRASEN
                                      __________________________
                                Name: Paul A. Strasen
                                Its:  Senior Vice President


[Corporate Seal]


Attest:

       /s/ Amy S. Powers
__________________________________
            Secretary

                                       8
<PAGE>

                                   EXHIBIT IB
                                   ----------

                               EXERCISE AGREEMENT
                               ------------------



To:                                                   Dated:

     The undersigned, pursuant to the provisions set forth in the attached
Warrant (Certificate No. W-___________), hereby agrees to purchase __________
shares of Common Stock covered by such Warrant for cash and makes payment
herewith in full therefor at the price per share provided by such Warrant.

                                Signature

                                _______________________________

                                Address

                                ________________________________


<PAGE>

                                   EXHIBIT II
                                   ----------

                                   ASSIGNMENT
                                   ----------


          FOR VALUE RECEIVED, ______________________________ hereby sells,
assigns and transfers all of the rights of the undersigned under the attached
Warrant (Certificate No. W-________________) with respect to the number of the
shares covered thereby set forth below, unto:


Name of Assignee:        _________________________________

                         _________________________________

                         _________________________________

Address:                 _________________________________

                         _________________________________

                         _________________________________

No. of Shares            _________________________________



          Accompanying this Assignment is a certificate from the proposed
transferee certifying that such assignment and Assignee meet the requirements of
Section 4 of the Warrant.

Dated:  ______________________  Signature:  ___________________________

                                            ___________________________

                                Witness:    ___________________________