Mix the flour, baking powder, sugar and vanilla sugar together. Pour melted butter over it and knead everything into crumbles. Press about 2/3 of the crumble mixture on the bottom of a springform pan (26 cm). Mix the remaining crumble with the brittle.
Peel the apples, quarter them, remove the core and cut into cubes. Mix with sugar, grated lemon zest and squeezed lemon juice and place on the crumble base. Sprinkle with the brittle crumble and bake the cake at 170 ° C for 55-65 minutes.