Beat the butter with the softened chocolate until fluffy.
Add the sugar, the egg yolks, the breadcrumbs, and the ground hazelnuts, mix well.
Whisk the egg whites to stiff peaks and gently fold into the batter.
Bake in a buttered, floured cake tin at 170°C for about 40-45 minutes.
For the icing, cook the sugar (twice the weight of the chocolate) with a little water into a slightly stringy syrup, then mix in the grated chocolate and butter.
Coat the cooled cake with the icing.
Based on: Malatinszky Fanny szakácskönyve (a classic Hungarian cookbook), modernised. Calories and protein are estimated.