• Preheat oven to 350F degrees.  Grease and flour 2 8-inch round cake pans.
• Beat egg whites until soft peaks form. Add 2 Tablespoons of sugar to the egg whites and beat on high speed. Add an additional 2 tablespoons of sugar and beat again until fully incorporated.  Set this aside
• In a large mixing bowl, beat the remaining sugar with flour, buttermilk, vegetable oil, baking powder, salt, and vanilla at low speed until combined.
• Divide cake batter into 2 bowls. In one bowl, mix in half of the egg whites.
• In the other bowl, mix in cocoa powder and 2 Tablespoons granulated sugar.  Then, beat in the other half of the egg whites. 
• Spoon half of the vanilla cake batter into each of the prepared pans. Spoon half of the chocolate cake batter into each pan by dropping batter in areas around the pan. Leave space between the areas with chocolate cake batter. Refer to photos for an example. Gently drag a butter knife through the batter to create the marble swirl.
• Bake for 25 minutes or until a toothpick comes out clean when inserted into the center, and cake bounces back when lightly pressed. Remove from oven and cool on wire rack. Let cake cool completely prior to frosting.

Chocolate Frosting

• To make the chocolate frosting, cream together shortening and butter in a large bowl.  Add the cocoa powder and vanilla to the bowl and mix. Beat in 2 cups of powdered sugar. Then, beat in 1-2 Tablespoons of milk to keep the frosting from getting too dry. Once the ingredients are well combined, add the rest of the powdered sugar and mix until combined. Stir in more milk, a teaspoon at a time, until desired consistency is reached.
• Place the first layer on a plate or cake stand and cover with chocolate frosting. Gently set the second layer on top of the frosted first layer, then finish by frosting the top and edges of the entire cake.