Preparation / Directions:
Preheat oven to 350 degrees. Prepare two 9" round cake pans with cooking spray and flour; set aside.
To prepare batter, combine cake mix, whipped topping mix, cocoa powder, and baking powder. In another mixing bowl, combine water, egg whites, oil, and one teaspoon vanilla extract. Mix dry ingredients with wet ingredients just until moistened. Bake for 25 minutes or until golden brown.
Meanwhile, to prepare frosting, combine remaining vanilla extract, whipped topping, and chocolate chips. Mix until smooth and melted. Remove 3/4 cup chocolate mixture; set aside.
While remaining mixture is still warm add candy bar pieces. Stir until combined, some will be chunky and some will be melted. When firm enough to spread, fill stack cake layers with half candy bar mixture.
Spread with remaining mixture evenly over top of cake. Frost sides with some of the reserved 3/4 cup candy bar mixture. Spread remaining chocolate mixture over top of cake. Refrigerate until ready to serve.