This is a fudgy cake that is very rich and there is more work involved than the usual marble cake.
Double Chocolate Marble Cake
1 cup butter
1 cup white sugar
1 cup packed brown sugar
1 teaspoon vanilla extract
1 cup sour cream
2 1/2 cups all-purpose flour
1/2 cup unsweetened cocoa powder
1/4 teaspoon salt
1 teaspoon baking soda
1/3 cup unsweetened cocoa powder
1/2 cup white sugar
1 Preheat oven to 325 degrees F (165 degrees C). Grease an flour one 10 inch tube pan.
2 To make marbling mixture: Combine 1/3 cup of the coca and 1/2 cup of the white sugar and mix well.
3 In a large bowl, beat the egg whites until stiff, and set aside.
4 In another bowl, cream the butter with 1 cup of the sugar and the brown sugar. Beat in the egg yolks, then the vanilla and sour cream.
5 In another bowl, stir together the flour, cocoa, salt, and baking soda. Beat into the creamed mixture. Stir about 1/3 of the egg whites into the batter to lighten it and then fold in the rest gently but thoroughly. Spread about 1/4 of the batter into a greased and floured tube pan and sprinkle with about 1/3 of the cocoa-sugar mixture. Continue repeating layers, ending with the batter. With a knife, lightly swirl the batter and cocoa mixture together
6 Bake at 325 degrees F (175 degrees C) for 1 3/4 hours, or until it tests done with a toothpick. Let cool on a rack. Makes 16 to 20 servings.