Combine the flour, 75 g sugar, 1 egg, and 125 g butter in small pieces. First, use the dough hooks of an electric mixer, then knead by hand until a smooth dough forms. Wrap the dough in cling film and chill for approx. 30 minutes
Peel, quarter, and core apples. Heat 1 tbsp butter, 50g sugar, and lemon juice. Add the apple quarters and simmer, covered, for 6-8 minutes. Transfer the apples to kitchen paper and let cool. Stir together the mascarpone, yogurt, and 150g sugar. Stir in 3 eggs, one at a time, then the custard powder and cornstarch.
Roll out the dough on a floured surface into a circle. Line a greased 26cm springform pan with the dough, pressing the edges firmly. Place the apples in the springform pan and spread the yogurt mixture over them. Bake in a preheated oven 350F for 50-60 minutes. Shortly before the end of the baking time, sprinkle the cake with flaked almonds. Remove the cake from the oven and loosen the edges. Let cool on a wire rack.
