For the buckwheat cake, separate the eggs. Cream butter and sugar until fluffy. Stir in the yolks one at a time.
Add buckwheat flour, nuts, vanilla sugar and baking powder and mix to a dough. Beat the egg whites with a pinch of salt until stiff. Fold into the dough.
Grease a springform pan and pour in the batter. Bake in the preheated oven at 160 °C for about 1 hour.
Cut the cooled cake in half and spread one half with currant jam. Place the lid on top. Melt the chocolate coating in a bain-marie and cover the buckwheat cake with it.