Melt the fat in a pot. Spread a springform pan (24 cm Ø) with a part of the fat and dust thinly with flour. Separate the eggs, beat the egg yolks and 125 g sugar with the whisk of the hand mixer until foamy.
Slowly stir in the remaining liquid fat. Add lemon zest and juice and beat again until foamy. Sift flour, salt and baking powder together. Beat the egg whites until stiff. Alternately fold flour and egg white into the egg yolk mixture.
Fill the dough into the springform pan and smooth it down. Peel, quarter, core and cut the apples on the upper side so that they still stick together at the bottom. Spread apples on the dough and sprinkle with the remaining sugar.
Bake in the preheated oven (electric cooker: 200 ° C/ circulating air: 175 °C/ gas: level 3) for about 40 minutes.