Grate 50 g dark chocolate coating. Melt butter and let it cool down a little. Mix flour, sugar, cocoa, vanillin sugar, salt and baking powder in a bowl.
Beat the eggs with the whisk of the hand mixer. Slowly allow butter to run in and stir in. Stir in the flour mixture with the whisks of the hand mixer, finally stir in the chocolate.
Put the dough into a greased and flour-sprinkled springform pan (26 cm Ø) and smooth it down. Bake in a preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: see manufacturer) for approx. 17 minutes.
Remove from the oven and let it cool down.
Finely chop 100 g of dark chocolate coating. Heat 6 tablespoons of espresso in a saucepan and dissolve the couverture in it, remove from heat and allow to cool slightly. Whip 500 g cream until stiff, stir 2 tablespoons into the chocolate mixture, then fold into the remaining whipped cream.
Pour the espresso cream on the cake base and spread it smooth. Chill the cake for about 10 minutes.
Spread the biscuits on the espresso cream and sprinkle with 100 ml espresso. Refrigerate the cake. Grate approx. 50 g of the milk chocolate with a peeler. Chop the remaining chocolate finely, melt over a warm water bath and let it cool down.
Whip the rest of the cream until stiff. Stir 2 tablespoons of whipped cream into the chocolate, then fold into the remaining cream. Spread the chocolate cream on the sponge cake and smooth it down. Chill the cake for about 5 hours.
Remove from the mould, place on a cake plate and decorate with chocolate shavings.