Separate eggs. Beat the egg whites and 4 tablespoons of lukewarm water until stiff. Add sugar and vanillin sugar bit by bit. Then stir in the egg yolks. Mix flour, cornstarch and baking powder.
Sieve onto the egg mixture and fold in loosely. Put the sponge mixture into a springform pan (26 cm Ø) lined with baking paper, smooth it down and bake in a preheated oven (electric range: 175 °C/ gas: level 2) for approx. 30 minutes.
Let it rest in the mould for a short time. Then remove from the mould and allow to cool completely on a cake rack. In the meantime soak the gelatine in cold water. Wash and drain the plums and, except for 2 pieces for decoration, stone them.
Bring the plums, juice, cinnamon stick, lemon juice, zest and sugar to the boil and cook for 5-10 minutes. Remove the cinnamon stick and lemon zest and finely puree the plums with the chopping stick. Pass through a sieve and dissolve the squeezed gelatine in the hot puree.
Chill until the fruit mass begins to gel. In the meantime cut the sponge cake base once. Place a springform pan rim or a cake rim around the bottom cake base. Whip the cream until stiff and stir into the plum puree.
Smooth the mixture on the lower cake base. Place the upper sponge cake base on top and chill the cake for at least 1 hour. In the meantime melt the white chocolate coating in a hot water bath. Spread thinly on a marble board and place in the freezer for a short time.
Then push thin rolls with a spatula. (The chocolate should not be too cold, but not too warm either!) Place the rolls on a plate immediately and place in the refrigerator until further use.
Whip cream and vanilla sugar until stiff. Remove the edge of the springform pan from the cake and spread 2/3 of the cream all around the cake. Pour the rest of the cream into a piping bag with a star-shaped spout and decorate the cake with cream tuffs.
Halve the remaining plums, stone them and cut them into thin slices. Decorate cream tuffs with it and put a lemon balm leaf in each of them. Sprinkle chocolate rolls in the middle of the cake. Makes about 16 pieces.