Mix sugar with 250 g flour and hazelnuts. Add the egg yolks and 250 g butter in pieces and knead into a crumbled dough with your hands. Put it in a cold place.
Clean and wash the rhubarb and cut into pieces of about 3 cm. Mix in jam. Puree milk and marzipan with a hand blender. Add vanilla cream powder and mix with the whisk of the mixer for about 1 minute.
Preheat oven (electric cooker: 180 °C/circulating air: 160 °C/gas: see manufacturer). Grease a springform pan (26 cm Ø) and dust with flour. Put half of the sprinkles in the mould, press it to a flat bottom and raise a small rim. Spread rhubarb mixture and pudding cream on top of it one after the other. Cover with the rest of the crumbles.
Bake in a hot oven for about 50 minutes. Remove the cake and let it cool down on a cake rack. Remove from the tin and dust with icing sugar.
This cake also tastes great with icing made from 100 g icing sugar and 2 tablespoons of milk.