Preheat the oven to 175 ° C top / bottom heat and grease the cake pan. First mix the liquid ingredients, then stir in the dry ingredients. Bake in the oven for about 1 hour.
Whip the cream firmly, add the cream stiffener and vanilla sugar and continue to beat. Finally mix in the chocolate flakes. Hollow out the cooled cake but leave enough edge and base thickness so that it remains stable. Then crumble the hollowed out and set aside. Cut the bananas into slices and top the cake. Liquefy Nutella with milk in a cup at 180 watts for 1 minute in the microwave. Then brush the bananas with it. Then apply the cream mixture in a dome shape and cover with the cake crumble at the end.
The cake tastes best when it has been through for a day.