Separating eggs. Beat the egg white and mineral water until stiff and finally add 150 g sugar. Beat the egg yolks one after the other. Mix flour, starch, cocoa and baking powder, sieve onto the egg mixture and carefully fold in. Pour the mixture onto a baking tray lined with baking paper (approx. 32 x 38 cm) and smooth it down.
Bake in a preheated oven (electric range: 200 °C/ convection oven: not suitable/ gas: level 3) for 10-12 minutes. Remove the finished sponge cake from the edge with a knife and turn out onto a damp tea towel sprinkled with 1 tablespoon of sugar. Carefully peel off the baking paper and let the sponge cool down. In the meantime soak the gelatine. Whip the cream until stiff, adding vanillin sugar, 60 g sugar and cappuccino powder. Squeeze the gelatine, dissolve it and stir it drop by drop into the cream. Spread half of the cappuccino cream on the sponge cake. Leave a 1 cm wide rim. Peel bananas and sprinkle with lemon juice. Dab the bananas dry and place them in 2 rows on the sponge cake.
Spread half of the cappuccino cream on the sponge cake. Leave a 1 cm wide rim. Peel bananas and sprinkle with lemon juice. Dab the bananas dry and place them in 2 rows on the sponge cake. Roll up the sponge cake from the long side. Spread with remaining cappuccino cream and chill for 2 hours. Decorate with chocolate rolls