Coarsely chop white and milk chocolate separately. Melt 100 g milk chocolate and white chocolate separately on a warm water bath. Spread the melted chocolate separately on a baking tray lined with baking paper and chill. Separate the eggs. Beat the egg yolks, salt and 60 g sugar with the whisk of the hand mixer until foamy. Mix flour, cornstarch and baking powder. Sieve onto the mixture and fold in carefully.
Beat the egg whites and 3 tablespoons of cold water until stiff. Also fold into the mixture. Fill the dough into a square springform pan (24 x 24 cm) lined with baking paper and smooth it down. Bake in a preheated oven (electric cooker: 200 °C/ convection oven: not suitable/ gas: level 3) for 7-8 minutes. Remove the cake from the oven and let it cool down on a cake rack. In the meantime soak the gelatine. Mix sour cream, quark, 60 g sugar and vanillin sugar. Halve the melons and remove the seeds with a tablespoon. Use ball cutters to cut out balls of different sizes. Cover the balls and put them in a cool place. Cut the remaining pulp from the skin and puree. Stir the melon puree into the sour cream mixture. Squeeze out the gelatine, dissolve and mix with 2 tablespoons of cream. Stir into the remaining cream.
Use ball cutters to cut out balls of different sizes. Cover the balls and put them in a cool place. Cut the remaining pulp from the skin and puree. Stir the melon puree into the sour cream mixture. Squeeze out the gelatine, dissolve and mix with 2 tablespoons of cream. Stir into the remaining cream. Fold in 50 g chopped chocolate. Pour the mixture onto the sponge cake base and chill for 2 hours. Remove the cake from the edge with a knife. Cover with melon balls. Mix the cake glaze, 2 tablespoons of sugar and apple juice with a wooden spoon. Bring to the boil while stirring. Sprinkle melons with cake glaze. Break the chocolate into pieces and decorate the cake with it
Pour the mixture onto the sponge cake base and chill for 2 hours. Remove the cake from the edge with a knife. Cover with melon balls. Mix the cake glaze, 2 tablespoons of sugar and apple juice with a wooden spoon. Bring to the boil while stirring. Sprinkle melons with cake glaze. Break the chocolate into pieces and decorate the cake with it