Separate eggs. Beat the egg whites and 1 tablespoon of water until stiff, then add sugar. Beat the egg yolks one after the other. Mix flour, cornstarch and baking powder, sieve onto the egg foam and fold in.
Line the bottom of a springform pan (26 cm Ø) with baking paper. Pour in the dough, smooth it down and bake in a preheated oven (electric: 175°C/ gas: level 2) for 20-25 minutes. Let it cool down.
Cut the sponge cake horizontally once and place a springform pan or cake rim around the bottom. Soak the gelatine in cold water. Sort the raspberries. Stir the quark, lemon juice and zest, sugar and 1 packet of vanilla sugar until smooth.
Whip 450 g cream until stiff. Squeeze out the gelatine, dissolve and mix with 2 tablespoons of quark mixture. Stir into the remaining quark, fold in the cream and spread 1/3 of it on the bottom sponge cake base.
Cover with 250 g raspberries and spread the remaining quark on top. Cover with the second sponge cake and put in a cool place for about 6 hours, preferably overnight. Whip the remaining cream and vanilla sugar until stiff.
Remove the cake from the edge of the mould with a knife and decorate with cream, remaining raspberries and lemon balm leaves. Dust with icing sugar. Makes about 12 pieces.