For the plum cake, separate the eggs, beat the egg whites with granulated sugar until stiff. Beat egg yolks, powdered sugar, vanilla sugar and whipped cream until fluffy. Mix in nuts, cocoa powder, spices and the rum.
Then add the flour and a dash of mineral water at the end, then fold in the beaten egg whites. Spread into a greased and floured baking pan.
Spread the plum halves on top, put some marzipan in the core hole and bake at medium heat.