Put the eggs and sugar in a mixing bowl and whisk with the whisk of the hand mixer on a hot water bath until thick and creamy. Sift flour, starch and baking powder over the mixture and fold into the mixture.
Line a baking tray with baking paper. Spread half of the sponge cake mixture on half of the baking tray. Sieve the cocoa powder over the rest, fold it in and spread it on the other half of the baking tray. Bake in the preheated oven (electric: 175 °C/ gas: level 2) for about 12 minutes.
Remove and turn over onto a damp cloth sprinkled with sugar. Remove the baking paper immediately. Roll up the sponge cake with the cloth and let it cool down. For the filling, soak gelatine in cold water.
Stir 2 tablespoons each of milk and sugar with the pudding powder until smooth. Boil up the rest of the milk. Stir in the whisked pudding powder and bring to the boil. Let it cool down a little bit and dissolve the squeezed gelatine in it.
Peel the bananas, sprinkle with lemon juice, puree and fold into the pudding. Cool until the mixture begins to set. Whip cream and remaining sugar until stiff and fold into the pudding, except for a little for decoration.
Spread the banana cream on the unrolled sponge cake and roll it up from the cocoa side. Refrigerate again for about 30 minutes. Pour the rest of the whipped cream into a piping bag with a star-shaped spout and squirt onto the roll.
Decorate with jelly bananas. Dust with icing sugar and cocoa. Sprinkle with chocolate. Makes about 12 pieces.