1 cup butter, softened
1 cup sugar
4 large eggs
1 teaspoon vanilla extract
1 cup all-purpose flour
1/4 cup unsweetened cocoa powder
1/2 teaspoon baking powder
1/4 teaspoon salt
Chocolate Frosting, recipe follows
Whipped cream, for topping, optional
1/4 cup butter
2 tablespoons unsweetened cocoa powder
3 tablespoons buttermilk
2 cups confectioners' sugar
3 (2.07-ounce) candy bars cut into 1/2-inch pieces (recommended: Snickers)