Separate eggs. Beat the egg whites and 1 tablespoon of water with the whisk of the hand mixer until stiff, add 75 g sugar and 1 packet of vanilla sugar. Beat the egg yolks one after the other. Mix flour, 25 g starch and baking powder, sieve onto the egg foam and fold in. Line the bottom of a springform pan (26 cm Ø) with baking paper. Fill in sponge cake mixture, smooth it down. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for about 20 minutes. Take out and let cool down
Remove the sponge cake from the tin, enclose it with a cake ring and sprinkle with 3 tbsp. egg liqueur. Soak gelatine in cold water. Mix quark, yoghurt, 150 g sugar and 1 packet of vanillin sugar until smooth. Squeeze the gelatine and dissolve in a small pot. Stir in 100 ml egg liqueur, then stir into the yoghurt quark cream. Chill the cream for about 10 minutes until it starts to gel. Whip cream until stiff and fold in. Pour the yoghurt quark cream on the base and smooth it down. Place the cake in a cool place for approx. 4 hours
Clean, wash and slice the rhubarb. Put half of the rhubarb in a pot with 100 ml water and cherry nectar, bring to the boil and steam over medium heat for about 10 minutes. Sweeten with 75 g sugar. Stir 2 level tablespoons of starch and 75 ml water until smooth, thicken the rhubarb with it and bring to the boil while stirring. Add the rest of the rhubarb, cook again for about 3 minutes while stirring and let it cool down
Remove the cake ring, arrange the cake on a plate. Before serving, spread the rhubarb compote on the cake and cut into pieces
waiting time approx. 5 1/4 hours