1
Whisk the egg whites until stiff. Slowly add the sugar and egg yolks. Stir in the flour and baking powder, cocoa, walnuts and melted margarine.
2
Mix and knead well. Place the dough on a baking tray and bake in a preheated oven at 200 degrees for about half an hour.
3
Meanwhile, prepare the cream. Whisk the eggs, sugar and coffee in a bowl. Heat the mixture slightly over a water bath, whisking in between, until the mixture thickens and foams.
4
Cool the cream slightly and then slowly stir in the melted butter, which should be about the same temperature as the cream.
5
Then return to the sponge cake. Cut the cooled one in two and moisten each part separately with coffee and rum. Spread with cream and ''stack'' the cake.
6
Weigh it down for about 10 minutes and then spread a layer of jam over it. For the icing on the cake, top with melted chocolate and decorate as desired.