Separate the eggs for the sponge cake. Beat the egg whites until very stiff. Beat the egg yolks, sugar and three tablespoons of cold water until frothy. Mix flour, starch and baking powder, sieve onto the egg yolk mixture and stir in.
Fold in the beaten egg white and halve the dough. Stir cocoa into one half of the dough. Spread the light and dark sponge cake mixture side by side on a baking tray lined with baking paper and bake in the preheated oven (electric range: 200 °C/ gas: level 3) for 15 minutes and let it cool down.
In the meantime, sort out gooseberries, clean, wash and boil them in a pot with 50 grams of sugar, vanillin sugar and 50 millilitres of water. Steam over medium heat for about five minutes.
Stir the starch and some cold water until smooth and add to the gooseberries. Bring to the boil again and let it cool down. Whip the egg yolks and remaining sugar until creamy. Gradually stir in the mascarpone, quark and lemon peel.
Cut out an equally large rectangle (approx. 30x23 cm) from the light and dark sponge cake. Cut the dark sponge cake rectangle into triangles. Dust one half with icing sugar, the other with cocoa.
Spread the stewed prickly liver compote over the light sponge cake. Spread mascarpone cream over it. Cover with the dusted triangles. Refrigerate for at least two hours.