Beat the eggs, salt, vanilla sugar and 125 g sugar until light creamy with the whisk of the hand mixer. Mix the ground hazelnuts, flour, cocoa and baking powder and carefully fold into the egg mixture.
Grease the bases of 2 springforms (each approx. 20 cm Ø) and spread the mixture on them. Place both moulds on a cake rack and bake in a preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: see
manufacturer) Bake for 20-25 minutes. Remove the moulds from the oven, remove the dough from the edge and let it cool on a cake rack.
Cut the nougat into small pieces. Heat 125 g whipped cream, melt nougat in it. Chill the cream nougat. Roast chopped hazelnuts in a pan without fat, then take them out and let them cool down. Caramelise 75 g sugar in a wide pot until golden brown.
Add 75 g whipped cream and butter and simmer for about 10 minutes. The result should be a thick, creamy caramel sauce. Let the sauce cool down while stirring occasionally.
Place the nougat cream in a bowl and stir until smooth. Stir in mascarpone, sour cream and icing sugar until a firmer cream is formed. Fold the roasted hazelnuts into 2/3 of the cream. Put the rest of the cream in a cool place.
Remove the nut shells from the moulds and cut them in half horizontally. Spread hazelnut cream on 3 bases. Place a cake ring around one base. Place the remaining finished cake bases on top. Finish with the last cake lid and chill for about 1 hour.
Remove the cake from the cake ring. Stir the rest of the cream again until smooth and spread it on the cake. Chill the cake for 2-3 hours. Before serving, decorate the cake with hazelnut flakes, caramel sauce and pralines.