Mix the butter with the sifted sugar and vanilla sugar until frothy. Gradually add the egg yolks. Mix the rum, lime juice, lemon zest and natural yoghurt and mix alternately with the sifted flour and baking powder. Beat the egg whites into snow and fold into the dough. Finally mix in the raspberries.
Grease and flour the Gugelhupf tin, pour in the batter and bake the Gugelhupf at 180 ° C for about 60 minutes. Let the Gugelhupf cool, turn it out and decorate with lemon glaze, raspberries, hazelnut brittle and halved lime slices.