How to make
Boil the starch according to package directions and add the vanilla. Once cooled, add the hazelnuts and the gelatin which you've soaked and melted in a water bath beforehand.
Cut 1 cake layer into cubes.
Pour a part of the cream into a silicone form, sprinkle on some of the layer cubes and banana slices, cream again, layer cubes, bananas, cream and cover with the whole layer (make a hole in the middle).
Leave it in the fridge to harden for a few hours.
Dip the form in hot water and invert it into a suitable plate.