For the dough, finely grate 50 g chocolate. Cream butter, sugar and vanilla sugar. Stir in eggs one after the other. Stir in grated chocolate. Mix flour, baking powder and cocoa and stir in alternately with the liqueur.
Pour the dough into a greased, flour-dusted ring cake tin (approx. 2 l capacity). Bake in the preheated oven (electric cooker: 175 °C/circulating air: 150 °C/gas: see manufacturer) for approx. 45 minutes. Turn out of the tin and let it cool down on a cake rack.
For the icing, divide 200 g of chocolate into pieces. Melt with oil in a hot water bath. Leave to cool a little. Spread the chocolate on the cake with a tablespoon (see tip below), leave to dry in a cool place for about 1 hour.
Sprinkle the chocolate all around the cake. Place baking paper underneath to catch the dripping off leftovers.