Separate the eggs. In a fat-free, cold container, beat the egg whites with a pinch of salt until stiff.
Beat egg yolks, room-warm butter, vanilla sugar and powdered sugar until very fluffy.
Sift the baking powder into the flour and mix with the nuts and grated chocolate.
Stir both masses together and mix in a small amount of the beaten egg whites until well blended. Finally, gently fold in the remaining beaten egg whites.
Line a baking tray with baking paper and spread the batter evenly. Bake in the oven preheated to 180 °C for about 25 minutes.
In the meantime, mix hot water and rum with powdered sugar.
Brush the still hot slices with jam and then coat with the rum glaze.
Let cool and cut into slices.