Sift together flour and baking powder. In a stand mixer, combine cubed butter, sugar, cocoa powder, and salt. Incorporate eggs, then flour and cream. Lastly add clarified butter.
Mix until smooth and transfer to a piping bag.
In a greased and floured 8″ x 4.5″ x 2.75″ cake tin, alternate piping layers of the vanilla cake batter and chocolate cake batter. Use the tip of a knife to swirl the batter to create the marbling effect.
Bake at 310°F for 50 minutes. Remove from oven and unmold quickly, then wrap in plastic wrap. Freeze the cake.