Preheat the oven to 325°F. Spray two 9-inch round cake pans with non-stick cooking spray (or use the wrappers from the butter to grease them thoroughly).

In one mixing bowl, combine the white cake ingredients: cake mix, butter, eggs, sour cream buttermilk and vanilla extract. Beat on low speed for 1 minute and then on medium-high speed for two additional minutes. Set aside.

In a second mixing bowl, combine the chocolate cake ingredients: chocolate cake mix, butter, eggs, sour cream buttermilk and vanilla extract. Beat on low speed for 1 minute and then on medium-high speed for two additional minutes.

Using an ice cream scoop or large spoon, pile dollops of cake batter into the pans, rotating between the white and chocolate cake mixes. Fill the pans about ⅔ of the way full to prevent overflowing - you may not use all of the batter. *See notes

Use a knife to cut through the batter and swirl the two colors. Do not over swirl which can result in the colors blending.

Bake for about 40 minutes or until a toothpick inserted into the cakes comes out with just a few crumbs (the pans are going to be more full than with a single cake mix, so the cook time will likely be 5-10 minutes longer than indicated on the box of cake mix.

Cool the cakes for 10-15 minutes and then remove the cakes from the pans and let them cool completely on a cooling rack.

Meanwhile, prepare the frosting. Chop the German chocolate baking bar into small pieces. Use a double boiler or 30-second increments in the microwave to melt the chocolate. Stir until fully melted and set aside to cool.

Use a whisk to stir together the cocoa powder and hot water (or hot cream) until smooth and shiny.

In a large mixing bowl, beat together the softened butter, cooled German chocolate, cocoa powder mixture, and powdered sugar. Beat until fully combined and fluffy.

Frost the bottom cake layer with about ½ cup of chocolate frosting. Stack the second cake layer on top of the first, top side down. Frost the top and sides of the cake with the remaining frosting.