For the fruit crumble cake, first prepare a dampfl for the yeast dough. To do this, stir the yeast with a little milk and a teaspoon of sugar until smooth, add 1 tablespoon of flour and cover the dampfl with a tea towel. Leave to rise in a warm place for about 30 minutes.
Preheat the oven to 180°C.
Peel apples and pears and cut into wedges or small cubes. Sprinkle with a little lemon juice to prevent them from turning brown.
To finish the yeast dough, melt margarine and stir it into the remaining milk. Add the flour, granulated sugar, egg, salt and milk mixture to the dampfl and knead into a smooth dough.Cover the yeast dough again and let it rest in a warm place.
For the crumbles, loosely mix the room-warm butter with flour, granulated sugar and vanilla sugar with your hands to make crumbs.
Line a baking sheet with parchment paper and press the yeast dough into the pan. Top with the apples and pears and spread the crumble on the cake.
Place the fruit crumble cake in the oven and bake for about 25-30 minutes. Allow to cool and serve.