Marmorkuchen - Marble Chocolate Cake

This is the 'official' version of the recipe, but in my family we use ground coffee instead of cocoa powder!

Ingredients

250 grams butter or margarine
250 grams caster sugar
1 sachet vanilla sugar (or a splash of vanilla essence)
3 - 4 eggs
a pinch of salt
1 vial of rum-aroma
500 grams flour
2 teaspoons baking powder
125ml milk (approx)
30 grams cocoa powder
25 grams sugar
2 - 3 tablespoons milk

Directions

Preheat oven to 180C / Gas Mark 4 / 350F. Using an electric whisk or a food processor, whisk the butter until frothy. Add the sugar, vanilla sugar (essence), eggs and rum aroma (if using) little by little. Start adding the flour and milk alternately and continue to mix. Only use enough milk to make a dough that drops of a spoon heavily.

Spoon 2/3 of the dough into a greased and floured Kugelhopf or loaf pan. (You could also use an angel cake pan or a springform pan with a fluted tube insert.) Add the cocoa powder and sugar to the remaining dough and mix until well combined. Add enough milk to once again achieve a dough that heavily drops of a spoon.
Spoon the dark dough over the light dough. Using a fork, marble the two doughs, by spirally dragging it through both.
Bake for 50-65 minutes. Test for doneness by inserting a wooden skewer into the middle. If it comes out clean the cake is done, if there is still dough sticking to the skewer it needs a little longer. Leave to rest for 5-10 minutes, before carefully turning out onto a cake rack to cool completely. Dust with icing sugar before serving.