Preheat oven to 325 degrees Fahrenheit.

Butter two 8-inch round cake pans.

Line the bottom of each pan with nonstick sprayed wax paper.

Lightly dust the pans with flour.

In a large bowl, mix butter and buttermilk (and the melted chocolate, if using).

If you don't have buttermilk, substitute by adding 1 teaspoon of lemon juice or vinegar to enough milk to make 1 cup.

In a separate bowl, add 1 cup of sugar to the egg whites and beat until stiff peaks form.

In another bowl, beat egg yolks with the remaining 1/2 cup of sugar until thick.

Add the yolk mixture to the buttermilk mixture.

Alternately add the egg whites (about a third at a time) and flour into the buttermilk/yolk mixture, gently folding to combine.

Stir until smooth, but be careful not to overmix.

Divide the batter evenly into the prepared cake pans.

Bake for 30 minutes, or until a knife inserted into the center comes out clean.

Cool in the pans for 5 minutes.

Remove the cakes from the pans and place them on a wire rack to cool completely.

Assemble the cake with your own frosting, or prepare the whipped cream topping.

To make the topping: Whip 2 cups of heavy cream with 3 tablespoons of sugar until stiff peaks form.

Spread about a quarter of the whipped cream between the cake layers.

Finish decorating the cake with the remaining whipped cream.

Sprinkle shredded chocolate evenly over the top and sides of the cake.