HEAT oven to 350ºF.
LINE 13x9-inch baking pan with foil, with ends of foil extending over sides. Grease foil.
MIX first 4 ingredients in large bowl. Stir in sugar and egg whites. Add flour and nuts; mix well. Spread into pan.
BAKE 25 min. or until toothpick inserted in center comes out with fudgy crumbs. (Do not overbake.) Cool completely. Use foil handles to lift brownies from pan before cutting to serve.