Preheat oven to 350°F. Spray an 8-inch square baking pan with cooking spray.
Stir cocoa, flour, baking powder and salt in a small bowl; set aside. Combine eggs, sugars, oil, butter and vanilla in a large bowl; blend with a wire whisk until smooth. Gradually stir in flour mixture, nuts and chocolate chips.
Bake for 25 to 30 minutes or until edges just begin to pull away from sides of pan. (Do not overbake.) Cool completely on wire rack.
HEART HEALTHY BROWNIE VARIATION: To reduce calories and saturated fat, substitute 2 egg whites for one of the eggs (or 4 egg whites for both eggs), and use 1/3 cup Mazola® Corn Oil instead of the butter and 1/4 cup corn oil. Omit chocolate chips.