Line a springform pan (26 cm Ø) at the bottom with baking paper. Separate the eggs. Beat egg white and 2 tbsp. water until stiff. Sprinkle 75 g sugar and vanillin sugar into the mixture. Beat the egg yolks separately. Sieve flour, starch and baking powder and fold in. Pour into the mould. Bake in the preheated oven (electric cooker: 175 °C / convection oven: 150 °C / gas: level 2) for 25-30 minutes. Allow to cool down
Soak the gelatine. Wash and clean the strawberries. Coarsely dice 250 g strawberries. Cut the rest of the strawberries into even slices
Mix champagne, liqueur, 50 g sugar and lemon peel. Squeeze the gelatine, dissolve over a mild heat. First mix with some sparkling wine, then stir into the rest of the sparkling wine. Cool until the mixture begins to gel
Cut the sponge in half horizontally. Place the edge of the mould around the lower base. Place the strawberry slices close to each other and close to the edge. Whip cream until stiff. Fold champagne jelly into the cream. Remove 1/4 of the cream. Fold the strawberry cubes into the remaining cream and spread on the sponge cake base. Cover with the top cake base and spread with the rest of the cream. Place the remaining strawberry slices on top in a flower shape. Chill the strawberry cake for 5-6 hours