Chop 250 g chocolate coating and melt over a hot water bath. Leave to cool slightly. In the meantime, mix oil, sugar, vanilla sugar and salt for 8 minutes with the whisk of the hand mixer until creamy. Stir in the eggs one by one. Add yoghurt and melted chocolate coating. Mix flour and baking powder and stir in briefly. Put the dough on a greased fat pan of the oven (32x39 cm) and smooth it down.
Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for about 50 minutes. Take out the cake and let it cool down. Finely chop 250 g chocolate coating. Bring the cream to the boil, melt the couverture in it and let it cool down for 30 minutes. Spread the cream and couverture mixture on the cake and let it get firm. Cut the cake into 35-40 pieces. Whipped cream tastes good with it