Line the bottom of a springform pan (26 cm Ø) with baking paper. Separate the eggs. Beat the egg whites, 3 tbsp. cold water and 1 pinch of salt until stiff, adding sugar and 1 vanillin sugar. Fold in the egg yolks one at a time.
Sift flour, starch and baking powder on top and fold in.
Spread the sponge mixture into the mould. Bake in the preheated oven (electric oven: 175°C/circulating air: 150°C/gas: level 2) for 25-30 minutes. Cool in the mould on a cake rack.
Soak gelatine in cold water. Cut the biscuit 1x horizontally. Close a cake ring around the lower cake base. Spread with jam.
Squeeze the gelatine and dissolve at low heat. Stir in elderflower syrup by the spoonful. Then stir into the Prosecco and chill for approx. 25 minutes until the Prosecco mass begins to gel.
Stir in between. Whip 400 g cream until stiff. Fold half the cream into the Prosecco mixture. Chill again for about 5 minutes, then fold in the remaining cream. Spread on the jam.
2. place the floor on top. Put it in a cold place overnight.
Whip 350 g cream and 1 vanillin sugar until stiff. Spread the cake with 2/3 of the cream. Sprinkle the cake edge with pistachios. Fill the rest of the cream into a piping bag (medium star-shaped spout). Decorate the cake with cream tuffs and sugar flowers.