Melt 75 g butter at low heat. Mix 500 g flour, 75 g sugar, vanilla sugar and 1 pinch of salt. Warm the milk lukewarm. Crumble yeast into it and dissolve it while stirring. Add yeast milk, liquid butter and egg to the flour mixture and knead to a smooth dough using the dough hooks of the hand mixer.
Cover and leave to rise in a warm place for about 45 minutes.
Grease the fat pan (approx. 32 x 39 cm; at least approx. 3.5 cm deep). Knead yeast dough again. Dust with a little flour and roll out on the fat pan, pressing up the edges by about 2 cm. Cover and leave to rise in a warm place for about 30 minutes.
Dice 125 g butter. Peel, quarter, core and roughly dice apples. Press larger depressions into the yeast dough with a tablespoon. Spread the apple and butter cubes in them. Sprinkle with 100 g sugar and bake in the preheated oven (electric cooker: 200 °C/circulating air: 175 °C/gas: level 3) for approx. 30 minutes.
Let it cool down.