The present invention relates generally to an accessory for a cooking appliance.  More particularly, the present invention relates to a griddle with a heat spreader for a cooking appliance such as a cooking range or a cooktop. 
Griddles are widely used on cooking appliances such as cooking ranges and cooktops.  As is known in the art, a cooking range or a cooktop typically has at least one surface heating unit.  A griddle, which is typically placed above one or more surface heating units of a cooking appliance, provides a substantially flat cooking surface.  When the outer case of a cooking appliance is made of stainless steel, the griddle is often made of stainless steel as well so that the griddle matches the cooking appliance in appearance. 
Stainless steel, however, does not have a very good thermal conductivity.  As is known in the art, to shorten the preheat time and to improve heat distribution for such a stainless steel griddle, a heat spreader made of a relatively high thermo-conductive material, such as aluminum or copper, can be attached to the bottom surface of the stainless steel griddle plate of the griddle.  The heat spreader can be metallically bonded or clad to the stainless steel griddle plate.  However, the resulting clad griddle has certain disadvantages.  For example, the clad griddle is relatively expensive to make.  In addition, when an aluminum heat spreader is clad with a stainless steel griddle plate, there will be stresses between the aluminum heat spreader and the stainless steel griddle plate when the clad griddle is heated, due to the different coefficients of thermal expansion of these materials.  Such stresses cause the clad griddle to bow, and may eventually break the bond between the aluminum heat spreader and the stainless steel griddle plate. 
Therefore, it would be desirable to provide a griddle which is relatively inexpensive to make, and which has a stainless steel griddle plate and a heat spreader, but the stress between the griddle plate and the heater spreader is substantially reduced when the griddle is heated.