Two-tone donut

Put in the mixer the butter and sugar: work it well then add the egg yolks one at a time. Add the flour, the egg whites and baking powder and vanilla. Place the mixture into two parts and unite in one part cocoa; grease and flour a mold. Pour first mixture yellow; then here and there that dark. When the cake is cooked you must see light and dark areas.

Bake at 220 degrees for half an hour and then increase the temperature for another 10 minutes. Before serving sprinkle with powdered sugar, to taste.