For the Devil’s Food Cake: 1/2 stick of butter, or 2 oz. (unsalted) 1 cup sugar 2 eggs, beaten until frothy and pale 1 and 1/2 cups cake flour 1 and 1/2 teaspoons baking powder 1/4 teaspoon salt 1/2 cup buttermilk or sour cream (or mix some milk with sour…