For the apricot cake with egg liqueur, beat egg whites with a pinch of salt until stiff. Beat yolks with powdered sugar, vanilla sugar and oil until foamy. Mix in the egg liqueur.
Mix in flour with Natrun. Wash and core the apricots, cut into small pieces and add to the yolk mixture. Carefully fold in the beaten egg white. Pour into a greased and floured baking pan.
Bake in the oven at about 170 °C. When the cake is almost done, sprinkle the grated marzipan on top and finish baking.