1Heat oven to 350° F. Spray nonstick cookie sheet with cooking spray. Place walnuts in food processor or blender. Cover and process, using quick on-and-off motions, until walnuts are consistency of coarse meal. Mix 1/2 cup of the ground walnuts and the remaining ingredients except egg whites in large bowl. Stir in egg whites thoroughly until stiff dough forms.
2Sprinkle remaining ground walnuts on cutting board or waxed paper. Divide dough in half. Shape each half into rectangle, 7x3 inches, on walnuts. Carefully transfer rectangles onto ungreased cookie sheet. Bake 15 minutes. Cut crosswise into 1/2-inch slices. Turn slices cut sides down on cookie sheet.
3Bake 10 to 15 minutes or until crisp and browned. Remove from cookie sheet to wire rack. Store tightly covered.