Beat the butter, powdered sugar and vanilla sugar until creamy. Gradually add the 8 egg yolks and the rum to the butter and stir in. Beat egg whites with 160 g sugar until stiff. Add the poppy seed mixture, hazelnuts and cinnamon to the butter mixture and stir in, fold in the egg whites. Pour the dough into a greased springform pan (26 cm). Bake in the preheated oven for about 30-45 minutes.
The poppy seed cake is super juicy and can easily be stored for several days.