Dissolve coffee powder in 4 tablespoons of boiling water. Leave to cool. Rinse raisins hot and drain. Mix the raisins and rum and leave to stand.
Separate the eggs for the sponge cake. Beat the egg whites and 1 pinch of salt until stiff, adding 125 g sugar and 1 packet of vanilla sugar. Stir in the egg yolks one by one. Stir in coffee. Mix flour, starch, cocoa and baking powder, sieve onto the egg mixture and fold in carefully. Spread the mixture on a baking tray (approx. 35 x 40 cm) lined with baking paper. Bake in a preheated oven (electric cooker: 200 °C/circulating air: 180 °C/gas: see manufacturer) for approx. 18 minutes. Let them cool down. Cut the sponge cake in half crosswise.
For the creamy quark, mix 75 g sugar and 1 sachet of vanilla sugar. Stir in mascarpone briefly. Fold in raisins and rum. Spread the cream on 1 sponge cake plate. Place the 2nd plate on top and press down gently. Chill for about 1 hour.
Finely grate the chocolate. Whip cream and 1 sachet of vanilla sugar until stiff. Spread the cream loosely on the cake and sprinkle with chocolate.