Beat the butter and sugar together until pale and creamy. Add the eggs one at a time, beating well after each one goes in. Sift in the flour and baking powder and beat well, then beat in the cream so that you have a fluffy mixture. Divide the batter between two bowls, putting more than half into one bowl. To this add the vanilla and beat it in well. Sift the cocoa into the other half, whisking it in completely.
Dollop most of the vanilla batter into the greased tin (you don’t have to entirely cover the bottom). Then dollop the chocolate batter in here and there, followed by the remaining