Beat the cold egg whites until they form soft peaks.

Add vanilla sugar, sugar, ground walnuts, cocoa powder and flour and mix until well incorporated.

Divide the batter into three and bake three cake layers. Use a baking tray lined with parchment paper greased on both sides.

Preheat the oven, and bake each layer at medium temperature. Check when it is done with the help of a knife; if the tip of the knife is clean, the cake layer is done.

Mix the sugar and egg yolks until they form a paste.

Add cocoa powder, softened butter and rum. Mix until well blended.

Coat the cooled cake layers with the cream filling, and sprinkle chopped chocolate over the top.
Set aside at room temperature for a couple of hours then refrigerate a little longer.