Separate eggs. Beat the egg whites and salt in a mixing bowl with the whisks of the hand mixer until stiff, adding 100 g sugar. Continue beating for about 1 minute. Stir in the egg yolks one after the other. Mix flour with baking powder, sieve onto the egg foam mixture and fold in carefully. Fold in 50 g grated chocolate. Line a baking tray (32 x 39 cm) with baking paper. Spread the mixture evenly on top and bake in a preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: see manufacturer) for approx. 10 minutes. Take out and let cool down.
In the meantime, for the compote, heat the plums with 100 ml juice, cinnamon, 1 packet of vanillin sugar and 100 g sugar in a wide saucepan, stirring occasionally, and bring to the boil over a medium heat. Stir the starch with the remaining juice until smooth, add to the plums while stirring constantly and simmer for about 2 minutes at low heat. Pour the compote into a flat bowl and let it cool down.
Soak gelatine in cold water. Stir curd and 100 g sugar until smooth. Beat 200 g cream until stiff. Squeeze gelatine well, dissolve in a small pot with 2-3 tbsp. cream, stir into the remaining cream and fold in 2 portions of cream and 50 g grated chocolate. Remove cinnamon from the compote, fold the compote into the cream.
Halve the sponge cake crosswise, place a rectangular cake frame around one half and spread cream evenly on top. Place the second sponge cake base on top and press down gently. Chill the cake for at least 3 hours.
Remove the cake frame before serving. Whip 300 g cream with 1 packet of vanilla sugar until creamy, fill into a piping bag, cut off the top so that there is a hole of about 1.5 cm. Spray cream as tuffs onto the cake. Cut the cake into about 10 pieces.