Beat 3 eggs, 50 g sugar and 1 packet of vanilla sugar until creamy on a hot water bath. Sift 50 g flour and 50 g starch on top and fold in. Spread it on a baking tray lined with baking paper.
Bake in the preheated oven (electric oven: 200 °C / gas: level 3) for 10-12 minutes. Turn onto a damp tea towel sprinkled with sugar. Peel off baking paper, cover sponge cake with a damp cloth and let it cool down.
Prepare dark sponge cake from remaining ingredients. For this, mix egg cream and melted fat and fold in cocoa and flour/starch mixture (same baking time). Warm up the nougat cream and spread it on the light-coloured dough.
Place the chocolate biscuit on top. Soak gelatine for the cream. Whisk 2 tablespoons of the milk, sugar and pudding powder and stir into the boiling milk. Leave to cool a little. Dissolve squeezed gelatine in it.
Let the pudding cool down. Peel 2 bananas, add lemon juice, puree, stir into the pudding and chill. As soon as the mixture begins to set, whip 150 g cream until stiff, fold in. Spread on the dark sponge cake.
Roll up from the long side, chill for about 1 hour. Sprinkle with icing sugar and chocolate shavings. Whip the rest of the cream until stiff, squirt onto the roll. Cut the remaining banana into slices, sprinkle with remaining lemon juice.
Serve the cake garnished with banana and mint. Makes about 16 slices.