Roughly chop the chocolate. Carefully melt fat and chocolate over a hot water bath. Leave to cool a little. Whisk eggs, sugar, vanilla sugar and salt with the whisk of the hand mixer for about 10 minutes until thick and creamy. Put the melted fat-chocolate mixture into a mixing bowl. Stir in egg-sugar cream.
Stir in sour cream. Mix flour and baking powder, sieve over it and stir in briefly. Soak the lady fingers with liqueur. Put half of the dough into a well-greased, flour-dusted saddle of venison dish (approx. 30 cm long). Place 2 rows of sponge fingers lengthwise on the dough, shortening the last ones if necessary. Add the rest of the dough and smooth it down. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for approx. 50 minutes. Let the cake rest in the pan for about 5 minutes, then remove from the pan and let it cool down on a cake rack. For the icing, chop the couverture roughly and melt over a hot water bath. Coat the cake with it and let it dry. Melt the white couverture over a hot water bath, pour onto a marble board and spread thinly.
Add the rest of the dough and smooth it down. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for approx. 50 minutes. Let the cake rest in the pan for about 5 minutes, then remove from the pan and let it cool down on a cake rack. For the icing, chop the couverture roughly and melt over a hot water bath. Coat the cake with it and let it dry. Melt the white couverture over a hot water bath, pour onto a marble board and spread thinly. As soon as the mixture has set, use a spatula to plane off thin shavings. Decorate the saddle of venison with it