Bring 220 ml milk and 1 tablespoon sugar to the boil. Stir pudding powder and 3 tbsp. milk until smooth. Stir into the boiling milk, bring to the boil and simmer for about 1 minute. Remove from the heat, pour into a bowl and cover with foil.
Leave the pudding to cool for at least 2 hours.
Cut the vanilla pod in half lengthwise and scrape out the pulp. Separate eggs. Beat the egg whites, vanilla sugar and 100 g sugar with the whisks of the hand mixer until stiff. Stir in egg yolks and vanilla pulp. Carefully fold in starch and flour.
Line the bottom of a springform pan (26 cm Ø) with baking paper. Fill in sponge cake mixture and smooth it down. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: see manufacturer) for 12-15 minutes.
Take out, turn onto a cake rack, remove baking paper, let the base cool down.
Roast the hazelnuts in a small pan without fat, take them out. Melt the nougat over a warm water bath. Cream butter with the whisk of the hand mixer, while slowly letting the nougat shrink.
Gradually fold in the room-warm pudding.
Cut the sponge in half horizontally. Place the bottom half on a cake plate and enclose with a cake ring. Spread 1/3 of the buttercream on top. Place the second sponge cake half on top. Spread half of the remaining cream on top.
Chill the cake for about 1 1/2 hours.
Roll out the marzipan into a circle (approx. 27 cm Ø) with the help of a dough roller on icing sugar. Cut out marzipan with a ring (26 cm Ø). Roughly chop the chocolate and melt over a warm water bath.
Carefully remove the cake from the ring and place the marzipan circle on top. Spread the edge of the cake with some cream. Pour the rest of the cream into a piping bag with a medium star-shaped spout. Spread the chocolate with a spoon in the middle of the cake.
Decorate cake with remaining cream and nuts.