For the blackberry and cream cake, beat the eggs with the sugar, vanilla sugar and salt until foamy. Sift flour with cocoa and fold loosely into the egg mixture. Spread on a baking sheet lined with baking parchment and bake quickly in the preheated oven at 220°C for about 5-6 minutes. After removing, immediately sprinkle with a little flour or sugar. Place a second sheet of baking parchment on top and turn out while still hot. Let the sponge cake cool between the baking paper so that it does not dry out.
Whip the whipped cream until stiff. Mix sugar, gelatin (prepared according to instructions) and lemon juice with the whipped cream mixture. Place part of the sponge mixture in a springform pan, spread with the whipped cream mixture and place another part of the sponge mixture on top. Top with blackberries and glaze with lukewarm blackberry jelly. Then refrigerate and decorate the blackberry and cream cake with a few blackberries before serving.