Mix flour, cocoa, baking soda and baking powder. Mix eggs, oil, buttermilk, 1 pinch of salt and sugar with the whisk of the hand mixer. Add the flour mixture in portions and mix to a smooth dough.
Grease 3 springforms (each 20 cm Ø) and dust with flour. Fill each springform pan with approx. 1/3 of the dough, smooth it down. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: see manufacturer) for about 30 minutes.
After about 15 minutes cover the cake with foil. Remove and let it cool down on a cake rack. Alternatively, bake the cakes one after the other.
Meanwhile, chop the chocolate and melt it over a warm water bath, stirring occasionally. Take off and let it cool down. Mix icing sugar, butter, nut nougat cream, sour cream and 1 pinch of salt with the whisks of the hand mixer to a smooth cream, add the still liquid chocolate in a thin stream and stir in.
Chill the cream for 20-30 minutes.
Remove the cake bases from the moulds and cut the surfaces straight. Place a cake ring around one base. Cut the chocolate cream in half. Put one half of the cream in a cool place. Spread about half of the remaining cream on the bottom cake base, smooth it down.
Place the second base on top, add the rest of the cream and smooth it down. Cover with the third base. Chill for about 1 hour.
Carefully remove the cake from the cake ring. Stir the rest of the chocolate cream through again and spread the cake all around, except for about 5 tbsp. for decoration. Pour the rest of the cream into a piping bag with a large star-shaped spout and squirt the tuffs onto the edge of the cake surface.
Decorate the middle of the cake with chocolate shavings.