Caramelise 100 g sugar in a pan without fat. Add the nuts and turn in it. Pour onto baking paper and allow to cool. Melt the fat and let it cool down a little. Mix flour, baking powder, vanillin sugar, salt and 300 g sugar.
Add fat and egg yolk and work into crumbles with the dough hooks of the hand mixer. Grease the oven pan (32 x 38 cm) and sprinkle with breadcrumbs. Press 2/3 of the crumbles into the pan.
Coarsely chop the brittle and mix it with the remaining crumbs, except for 4 tablespoons. Peel, quarter, core and cut apples into slices. Mix with 50 g sugar, lemon juice and zest and spread on the base.
Add the brittle crumbles and bake in the preheated oven (electric range: 175 °C/ convection oven: 150 °C/ gas: level 2) for 50-60 minutes. Leave to cool on a rack. Cut into 24 pieces, sprinkle with remaining brittle and serve.
Whipped cream tastes good with it.