Chocolate Cake with Whipped Cream Chocolate Frosting

This is a family favorite from the time I was a little girl. I think it is best when used with a dark chocolate cake mix.

Whipped Cream Chocolate Frosting

2 cups (1 pint) heavy whipping cream
1/3 cup sugar
3 tablespoons baking cocoa
1 teaspoon vanilla
(Optional: add just a touch of instant coffee for a slight mocha flavor, perhaps a 1/4 teaspoon)

Mix (do not whip) all ingredients in a bowl. Cover and set in your refrigerator to chill for at least 2 hours. Longer is OK. (Place your beaters in the freezer.) Then beat the mixture until it is so thick it holds its shape and will stand in peaks.
This makes enough frosting for the top, sides and between the split layers even if you use a generous hand.
Allow the cake to chill well through before serving.
Garnish with grated chocolate or chopped walnuts.