Marble a vanilla cake batter with cocoa and bake in a large tin until done.

Steps

1. Cream butter and sugar.
2. Sift dry ingredients — flour and baking powder.
3. Add eggs one by one — beat well.
4. Add dry ingredients alternately with milk.
5. Remove half of the mixture and add the cocoa mixture (cocoa, 1/4 cup sugar, water and rum).
6. Grease large tin — 10 inch and spread a layer of white mixture, then a layer of cocoa mixture; finish with cocoa mixture.
7. Swirl the whole and bake at 350°F for about an hour or when tested the tester comes out dry.