Preheat oven to 160° and prepare your baking tin. cream the batter and the sugar. Add the eggs one at a time as you beat. Fold in the flour, milk and vanilla until the mixture is smooth. Divide the mixture. Add cocoa powder to one part of the mixture and mix.

Put your batter into the tin, alternating the plain batter with the coloured batter to have layers and spread well. Bake for 55 minutes or until a skewer inserted comes out clean.