Roughly chop 120 g of couverture. Melt with 125 g butter on a hot water bath. Separate the eggs. Beat the egg whites until stiff and add 20 g of sugar at the end. Beat the egg yolks and 100 g sugar until frothy.
Gradually pour the dissolved couverture-butter mixture into the egg yolk while stirring. Mix hazelnuts, flour and baking powder and stir into the chocolate mixture. Then carefully fold in the beaten egg white in two portions.
Grease the bottom of a springform pan (26 cm Ø) and sprinkle with breadcrumbs. Pour in the dough, smooth it down and bake in a preheated oven (electric: 175 °C/ gas: level 2) for approx. 25 minutes.
Let the base cool down well on a cake rack. Meanwhile, for the caramel buttercream, stir pudding powder, 60 g sugar and approx. 1/8 litre milk until smooth. Bring the remaining milk to the boil, remove from the heat and stir in the pudding powder.
Boil the pudding again for at least 1 minute while stirring, place in a bowl and cover with cling film. Let it cool down. Caramelise the remaining sugar in a pan until golden brown.
Add 10 g butter and hazelnut kernels and mix well with the caramel mass. Coat a piece of aluminium foil with oil and let the nuts cool down on top. Cut the chocolate base once and place the edge of the mould around the bottom base.
Whip the rest of the room-warm butter with a kitchen machine until white-frothy. Also stir in room temperature pudding by the spoonful. Spread about 2/3 of the cream on the base and cover with the second base.
Spread the rest of the buttercream loosely on top and put the cake in a cool place for about 3 hours. Coarsely chop the hazelnut brittle, melt the rest of the couverture on a hot water bath and put it in a small freezer bag.
Sprinkle the cake with hazelnut brittle and remove from the cake ring. Cut a small corner from the freezer bag and decorate the cake with strips. Refrigerate for another 30 minutes. Makes about 16 pieces.