Mix cocoa and approx. 175 ml boiling water to a creamy mixture. Let it cool down. Separate the eggs. Beat the egg yolks in a large bowl, add 300 g sugar and vanillin sugar and beat everything for about 10 minutes until creamy.
Briefly stir in the quark, pudding powder and lemon zest. Stir the cocoa mass under 1/3 of the cheese mixture. Beat the egg white in 3 portions until stiff, adding 2 tablespoons of sugar to each. Fold 2 portions of beaten egg white into the light cheese mixture and fold 1 portion of beaten egg white into the dark cheese mixture.
Grease the oven pan (approx. 32 x 39 cm) and sprinkle with breadcrumbs. Spread light-coloured cheese mixture on top. Spread dark cheese mixture as a blob on top. Pull both masses through spirally with a fork.
Bake in the preheated oven (electric oven: 175 °C/ gas: level 2) for about 1 hour. Let it cool down. Whip cream until stiff. Cut the cake into about 32 triangles. Decorate with cream tuffs. Break the chocolate into pieces, melt in a hot water bath and let it cool down a bit.
Use a spoon to spread as strips on the cream tuffs. Allow to set.