Transfer to large bowl. Cut carrots into pieces about 2 inches long. Slice pieces lengthwise. Stack slices and cut into thin lengthwise strips. Peel celery with vegetable peel to remove strings.
Slit leek twice lengthwise from center of white part upward.
Flatten each piece and cut into thin strips. Put strips in bowl of cold water to rid them of any remaining sand. In medium saucepan, bring 2 cups stock to boil. Add vegetables and return to boil. Cover and cook over low heat until vegetables are crisp-tender, about 5 to 6 minutes.