Preheat the oven to 175 ° C (convection). Peel, quarter and core the apples and pears, dice finely. Squeeze the lemon and drizzle the juice over the fruit.
Separate the eggs, beat the egg whites with vanilla sugar and salt until stiff. Mix the egg yolks with 120 g sugar, yogurt, quark and pudding powder. Fold in the egg whites. Line a springform pan (26 cm) with baking paper. Pour in the curd mass.
Melt the butter, knead with the sifted flour and the remaining 80 g sugar and the almond flakes until crumbly. Spread the fruit and the crumble on the curd mixture.
Bake the cake on the middle rack for about 50 - 60 minutes. Allow to cool in the mold. Dust with powdered sugar if necessary.