Beat butter with sugar and salt and lemon peel,add egg yolks one at a time.whip the egg whites with sugar until very stiff.

Combine part 1$2 and fold in the flour with baking powder with part3.take a third of the mixture aside and blend the cocoa powder and milk mixture together.

Fill first some white mixture into the cake tins then the chocolate mixture on top and fill with the remaining white mixture.bake for 180 degrees