Wash, peel and core apples and cut them into thin slices. Select the blackberries, wash and drain well. Mix apples and berries and place in an ovenproof dish. Sprinkle with 20 g sugar
Coarsely chop the hazelnuts. Knead flour, 125 g sugar, fat, oat flakes and nuts in a bowl first with the dough hooks of the hand mixer, then with your hands to a crumble dough. Spread the dough evenly over the fruit. Bake in a preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: see manufacturer) for 35-40 minutes until golden brown and the fruit will bubble. Serve with whipped cream or vanilla ice cream