Frosted Chocolate Brownie Supreme

-----CHOCOLATE BROWNIES----- 1/2 c (+ 3 Tbsp.) Reduced-calorie

. margarine, softened 1 1/3 c Sugar

8 ea Egg whites

1/2 c Nonfat sour cream

1/3 c Evaporated skim milk

2 ts Vanilla extract

1 1/3 c All-purpose flour

1 t Baking powder

1/2 ts Salt

2/3 c Unsweetened cocoa

Vegetable cooking spray Creamy chocolate frosting