Cake:7 large eggs, separated1/2 cup of baking cocoa3/4 cup of boiling water1 and 3/4 cups of cake flour1 and 3/4 cups of sugar1 and 1/2 teaspoons of baking soda1 teaspoon of salt1/2 cup of canola oil2 teaspoons of vanilla extract1/4 teaspoon of cream of tartarIcing:1/3 cup butter2 cups of confectioners sugar2 ounces of unsweetened chocolate, melted and cooled1 and 1/2 teaspoons vanilla extract3 to 4 tablespoons of hot waterChopped nuts, optional