For the chocolate plum cake, first separate the eggs. Beat the egg whites with a pinch of salt until stiff. Melt the chocolate in a water bath. Beat egg yolks, powdered sugar, vanilla sugar, melted chocolate, spices and whipped cream until fluffy.
Mix in the egg liqueur and flour. Fold in beaten egg whites and spread into a greased and floured pan.
Bake briefly at medium heat, then spread the halved and pitted plums on the cake and finish baking.