Beat the fat, sugar and vanilla sugar until frothy. Stir in eggs one at a time. Mix the flour and baking powder and stir into the fat and egg mixture. Stir milk into the batter, except for 2 tablespoon. Halve the dough. Stir in half of the cocoa and the rest of the milk.
Drain the tangerines. Grease a springform pan with a tube bottom insert. First pour in the light batter, then spread the tangerines on top and then pour in the dark batter. Using a fork, pull it in a spiral through the layers of dough. Bake the cake in the preheated oven to 175 degrees for 50 - 55 minutes.