Butter a bundt cake tin and flour it
Prepare the two cake mix separately according to the instructions on the packaging
Spread ¾ of the vanilla batter in the mold and pour the third of the chocolate batter in the center of the vanilla batter and using a spoon lightly mix the two batters in circular motions.
Bake at 350F for about 45 minutes
Meanwhile prepare the icing according to the instructions on the package
Allow the cake to cool before creaming it