Separate 3 eggs. Beat 3 egg whites and 3 tablespoons of water until stiff. Add sugar and 1 vanillin sugar at the end. Fold in the egg yolks one after the other. Sift the flour, starch and baking powder into the egg foam and fold in. Spread the mixture into a springform pan lined at the bottom with baking paper. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for approx. 20 minutes, let cool down
Cut the sponge cake once, place the cake ring around the bottom cake base. Soak the gelatine. Chop the chocolate, melt. Separate remaining eggs. Beat 2 egg whites and 200 g cream separately until stiff. Cream the whole egg yolk, 1 tablespoon sugar and the rest of the vanillin sugar. Stir in chocolate. Squeeze the gelatine, dissolve and stir into the chocolate mixture. First fold cream, then beaten egg white into the chocolate mousse. Spread the sponge cake base with it, chill for about 15 minutes. Cover with the 2nd base, refrigerate for approx. 4 hours
Chop the couverture, melt it. Place baking paper on the kitchen board, spread an even thin layer of chocolate coating. Put in a cool place. Whip the rest of the cream and sugar until stiff. Remove the cake from the ring and spread with cream. Cover generously with blackberries. Turn the chocolate coating over onto the board, remove the paper. Break the chocolate plate into pieces and press them onto the edge of the cake. Put in a cool place. Serve dusted with icing sugar