Beat the fat, sugar, vanillin sugar and salt with the whisk of the hand mixer until foamy. Stir in the eggs one after the other. Mix flour and baking powder and stir into the fat egg mass.
Stir the milk, except for 2 tablespoons, into the dough. Halve the dough. Stir in half the cocoa and the remaining milk. Drain the mandarins and collect the juice. Fold mandarins, except for some for decoration, into the light half of the dough.
Grease a springform pan with a tube bottom insert (26 cm Ø) and sprinkle with breadcrumbs. First fill in the light dough, then the dark dough. Use a fork to pull spirally through the dough.
Bake the cake in the preheated oven (electric: 175 °C/ gas: level 2) for 50-55 minutes. Remove from the tin and let cool on a cake rack. Stir icing sugar and 3-4 tablespoons of mandarin juice until smooth.
Spread the cake with it. Decorate with the remaining mandarins and bark chocolate. Makes 16 pieces.