Chop 150 g dark chocolate and melt over a warm water bath. Place the cherries in a sieve, collecting the juice. Cream butter, sugar, vanilla sugar and salt with the whisk of the hand mixer.
Stir in the eggs one by one. Mix flour and baking powder and stir in alternately with milk.
Cut the dough in half. Stir into one half of liquid chocolate. Mix the other half with 5 tablespoons cherry juice and 1 tablespoon flour and fold in the cherries. Fill both doughs alternately in strips into a greased springform pan (24 x 24 cm Ø) dusted with flour and swirl slightly with a fork.
Bake in a preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: see manufacturer) for approx. 50 minutes, remove from oven and let cool on a cake rack.
Chop 150 g dark chocolate and light chocolate separately and melt over a warm water bath. Carefully remove the cake from the mould and place on a cake platter. Spread the dark chocolate on the surface.
Pour the light chocolate in strips on top, pull through with a wooden stick. Leave to dry.