Warm 5 tablespoons of milk lukewarm. Crumble the yeast into a bowl. Mix with 1 teaspoon of sugar and 5 tablespoons of lukewarm milk. Cover and leave to rise in a warm place for about 15 minutes.
Wash and dry the lemon and grate the peel. Melt 80 g fat and add the remaining milk. Put 500 g flour, egg, 70 g sugar, lemon rind and salt in a bowl. Add yeast dough and lukewarm milk-fat mixture.
Work into a soft dough with the dough hooks of the hand mixer. Cover and leave to rise in a warm place for about 30 minutes. In the meantime, halve the lemon and squeeze the juice. Wash, peel and quarter apples, remove core.
Cut quarters into slices and sprinkle with lemon juice. For the crumbles, melt 175 g fat. Mix 250 g flour, 200 g sugar and vanillin sugar in a bowl. Add hot fat and work everything into coarse crumbles.
Grease a baking tray (39 cm x 32 cm). Knead the yeast dough again and roll out on the baking tray. Spread apple slices on it and sprinkle with the crumbles. Let it rise for another 10-15 minutes.
Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for 35-40 minutes. Whipped cream tastes good with it.