Marble Cake from the Göflaner Alm mountain pasture

Mix the butter with 200g sugar and vanilla sugar, gradually add the egg yolks. Add two tablespoons of flour, followed by the milk and the lemon flavouring. Beat the egg whites with the remaining sugar and a pinch of salt until stiff. Fold the beaten egg whites, flour and baking powder into the butter mixture. Divide the mixture in half. Mix one half with the cocoa and rum. Pour half of the light-coloured mixture into the prepared cake tin, then a layer of the dark mixture and finally the remaining light-coloured mixture.
Bake at 180° for 50-60 minutes.

Variation:
To make a raisin cake, omit the chocolate and rum and add 100g raisins and more lemon flavouring to the mixture.