Flora's Recipe Hideout: Frosted Chocolate Brownie Supreme (Low-fat)

Ingredients

• 1/2 cup reduced-calorie margarine, softened
• 3 tablespoons reduced-calorie margarine, softened
• 1 1/3 cups Sugar
• 8 Egg whites
• 1/2 cup Nonfat sour cream
• 1/3 cup Evaporated skim milk
• 2 teaspoons Vanilla extract
• 1 1/3 cups All-purpose flour
• 1 teaspoon Baking powder
• 1/2 teaspoon Salt
• 2/3 cup Unsweetened cocoa
• Vegetable cooking spray
• 3 cups Sifted powdered sugar
• 1/4 cup Unsweetened cocoa
• 1/4 teaspoon Salt
• 1/4 cup Skim milk
• 1 1/2 teaspoons Vanilla extract