For the yeast dough melt 75 g butter and let it cool down a little. Mix 500 g flour, 75 g sugar, vanilla sugar and 1 pinch of salt. Warm the milk lukewarm. Crumble the yeast into it and dissolve it while stirring.
Add yeast milk, egg and liquid butter to the flour mixture. Knead everything with the dough hooks of the mixer to a smooth dough. Cover the dough and let it rise in a warm place for about 45 minutes.
Grease a fat pan (deep baking tray; approx. 32x39 cm). Knead yeast dough on a little flour with floured hands. Roll out on the fat pan, if necessary press the edges with your hands. Cover the pan and leave to rise in a warm place for about 30 minutes.
In the meantime peel the apples, quarter them, remove the core and dice them roughly. Dice 125 g cold butter. Preheat the oven (electric cooker: 200°C/circulating air: 175°C/gas: level 3). Press larger depressions into the yeast dough with the back of your hand.
Spread apples and butter cubes in it. Sprinkle with 100 g sugar. Bake in a hot oven for about 25 minutes.