Preheat oven (electric cooker: 200 °C/circulating air: 175 °C/gas: see manufacturer). Grease an ovenproof dish. Peel, quarter, core and cut apples into slices. Distribute in the form. Pre-bake in a hot oven for approx. 10 minutes.
For the crumbles, melt 200 g butter. Coarsely chop the nuts. Mix flour, sugar, vanilla sugar, muesli and pecans in a bowl. Add liquid butter and mix with your hands to coarse S
Sort the blackberries, rinse briefly. Remove apples from the oven. Spread the blackberries and crumbles on the apples. Continue baking at the same temperature for 20-25 minutes. Serve with semi-stiff whipped vanilla cream.