Roast 200 g ground hazelnuts in a pan without fat until golden brown. Take out and let cool down. Beat the eggs, 200 g sugar and 1 packet of vanilla sugar until creamy. Mix the roasted nuts, flour, salt and baking powder and stir in briefly. Line the bottom of a springform pan (26 cm Ø) with baking paper, fill in the dough and smooth it down. Bake in a preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for approx. 35 minutes.
Remove and let cool on a cake rack. In the meantime, line a tray with aluminium foil and brush with oil. Melt 75 g sugar in a pan until it is golden brown. Stir in whole nuts. Quickly place small heaps on the prepared tray and let them solidify. Remove the cake from the tin and remove the baking paper. Carefully cut the base twice horizontally. Whip the cream until stiff, while allowing 3 sachets of vanilla sugar to trickle in. Finally, add the cream thickener. Fill 75 g cream into a piping bag with perforated spout and set aside. Spread 1/3 of the cream on the bottom cake layer, place the middle layer on top and spread with another 1/3 of the cream. Place the 3rd cake layer on top and spread the rest of the cream on the cake.
Whip the cream until stiff, while allowing 3 sachets of vanilla sugar to trickle in. Finally, add the cream thickener. Fill 75 g cream into a piping bag with perforated spout and set aside. Spread 1/3 of the cream on the bottom cake layer, place the middle layer on top and spread with another 1/3 of the cream. Place the 3rd cake layer on top and spread the rest of the cream on the cake. Spray the cream tuffs onto the cake with the piping bag. Chill for about 2 hours. Sprinkle with 50 g ground hazelnuts and decorate with hazelnut brittle