Separate eggs. Beat egg whites and 3 tablespoons of water until stiff. Finally, pour in 100 g sugar and vanillin sugar. Beat the egg yolks one after the other. Mix flour, cornstarch 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 the dough and smooth it down. Bake in the preheated oven (electric: 175 °C / gas: level 2) for 25-30 minutes. Let the sponge cake cool down, then cut through the base so that the lower base is slightly thicker.
Soak gelatine in cold water. Drain mandarins on a sieve. Squeeze the gelatine, dissolve it and mix it with the passion fruit juice and the remaining sugar. Put in a cool place. Whip 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. Refrigerate 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.