Preheat the oven to 180°C, butter and flour 3 cake tins (or use one tin and bake the batter in 3 batches).
Whisk the egg whites to stiff peaks, fold in the 250 g sugar, then gently fold in the ground hazelnuts and almonds.
Divide the mixture into three equal parts, smooth into the tins, and bake for about 20-25 minutes until golden. Let cool completely.
For the filling, beat the butter with the chocolate and egg yolks until smooth.
Cook the 100 g sugar with a little water until a drop in cold water forms a soft ball (about 115°C), then let cool and add to the butter-chocolate mixture.
Stir in the toasted ground hazelnuts, then chill the cream until firm.
Fill and thinly coat the cake with the cream.
Sprinkle the top with white almond slivers toasted golden in the oven.
Based on: Malatinszky Fanny szakácskönyve (a classic Hungarian cookbook), modernised. Calories and protein are estimated.