Separate eggs. Beat egg whites and 3 tbsp. water until stiff. Finally, pour in 100 g sugar and vanillin sugar. Fold in egg yolks one after the other. Mix flour, starch and baking powder, sieve onto the egg foam and fold in loosely.
Line the bottom of a springform pan (26 cm Ø) with baking paper. Fill in sponge cake mixture and smooth it down. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: see manufacturer) for 25-30 minutes.
Let the sponge cake cool down.
Cut through the bottom so that the lower bottom is a little thicker. Soak the gelatine in cold water. Drain mandarin oranges on a sieve. Squeeze the gelatine, dissolve it and mix it with the passion fruit juice and 50 g sugar.
Whip the cream until stiff. When the fruit juice begins to gel, stir about 2/3 into the cream. Fold in the mandarins. Then fold the remaining fruit mass as "streaks" into the cream. Chill again briefly.
In the meantime, crumble the thinner soil. Spread the passion fruit cream on the thicker sponge cake base like a dome and smooth it down. Sprinkle with sponge flakes, press on and refrigerate for about 3 hours. Dust with icing sugar shortly before serving.