Grate 50 g chocolate. Cream butter, sugar and vanilla sugar with the whisk of the hand mixer. Stir in the eggs one by one. Stir in grated chocolate. Mix flour, cocoa and baking powder and stir in alternately with the liqueur.
Pour the dough into a greased, flour-dusted ring cake mould (approx. 24 cm Ø, 2 litres capacity). Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: see manufacturer) for approx. 45 minutes.
Remove and let it cool down on a cake rack.
Chop 200 g chocolate and melt over a warm water bath. Stir in the oil thoroughly and let it cool down for about 5 minutes. Remove the cake from the tin and place it on a cake plate. Spread the icing on the cake with a tablespoon.
Leave to dry for about 1 hour in a cool place.