Beat the yolks, sugar and vanilla sugar until thick and creamy. Whip the egg whites until very firm and fold into the yolk mixture alternately with the flour. Spread the sponge mixture on a baking sheet lined with parchment paper and bake in a heated oven at 200 °C for about 10 minutes. Turn out onto a moistened tea towel, remove the paper. Roll up loosely, place on a sugared board.
Roll up the cooled roulade, spread with two thirds of the chocolate cream, cover the bottom edge with peeled whole bananas and roll up tightly. Spread outside with remaining creme, sprinkle with shaved chocolate.
Cream: Cream butter, soften chocolate in bain-marie and add to butter alternately with remaining ingredients, stir until very creamy.
Tip: Feel free to use better chocolate – the more delicious the result!