Mix the flour with powdered sugar, a pinch of salt, vanilla sugar and baking powder. Add cubed butter at room temperature, one egg and knead a smooth dough, which you wrap in a food foil and put in the fridge for 1 hour.
Pour 1 cup of milk into a bowl, add the pudding powders and beat them thoroughly so that there are no lumps. Put the remaining milk on the stove and bring it to a boil. When the milk boils, add granulated sugar and let it dissolve. When the sugar has dissolved, add milk with pudding, chocolate broken into cubes and cook a thick cream, then set aside. Add the butter to the hot pudding and melt it by stirring. Cover the pot with the pudding with a food foil or a lid to prevent a crust from forming and let it cool.
Chop the hazelnuts into smaller pieces.
Take the chilled dough out of the fridge and divide it into 2 parts. Roll out one part to the size of a baking sheet (approx. 10 x 14 in'). Line the baking sheet with baking paper and place the rolled out dough. Layer the chocolate pudding on top of it. Smooth it well and sprinkle it with chopped hazelnuts. Grate the second half of the dough on a coarse grater and sprinkle on top.
Put the cake prepared in this way into a preheated oven and bake for 40 minutes at a temperature of 355 °F / 180 °C. Take it out and let it cool down. The top can be sprinkled with powdered sugar or grated chocolate. Enjoy!
