Grease the saddle of venison dish (30 cm long; approx. 1 l capacity) or box dish (30 cm long) and dust with flour. Break chocolate into pieces. Dice butter. Melt both together in a hot water bath. Let cool down a little bit
Beat the eggs, sugar, vanillin sugar and salt for about 8 minutes until fluffy. First stir in the chocolate mixture, then the sour cream. Mix flour and baking powder, then sieve and stir in briefly
Drizzle ladyfingers with liqueur. Spread half the dough into the mould. Place 2 rows of ladyfingers on the dough with some distance between them lengthwise. Spread the rest of the dough on top
Bake in the preheated oven (electric oven: 175 °C/circulating air: 150 °C/gas: level 2) for about 50 minutes. Cool down for about 10 minutes. Turn out of the tin, let cool down
Roughly chop the remaining couverture. Melt the white one in a hot water bath. Spread it thinly, e.g. on a marble slab and let it dry. Plane off in long shavings. Melt the rest of the couvertures together in a hot water bath. Coat the cake with it. Sprinkle with the shavings. Let it dry.