For the apple-cheese crumble cake, mix well the flour, sugar, lemon sugar, and then add the melted butter. Work everything into crumbles (works well with the dough hook). Then sprinkle the crumble with a little flour.
Grease a springform pan (26 or 28 cm) and press 2/3 of the crumble firmly onto the bottom. Smooth the applesauce over the top.
For the topping, cream the soft butter, add the sugar, lemon sugar and juice and mix well. Then add the eggs and beat until creamy. Stir in the curd and custard powder and spread this mixture over the applesauce. Spread the remaining crumble around the edges and possibly in the middle.
Bake in the preheated oven at 200 °C on the lowest rack for about 50 minutes (watch!). Allow to cool slightly, remove from the pan, sprinkle with powdered sugar and serve the apple and cheese crumble cake.