Peel 3 apples, quarter them, remove the core and dice the flesh. Add 25 g sugar and lemon juice and mix together. Whip butter and 150 g sugar with the whisk of the hand mixer until creamy.
Add the eggs one by one and stir in.
Beat the double cream until stiff, add to the butter egg mixture and stir in. Mix flour and baking powder and stir in by the spoonful. Fold in apples. Pour the dough into a greased and floured box form (approx. 11 x 30 cm) and smooth it down.
Peel the remaining apple, quarter it, remove the core and cut the fruit flesh into thin slices with a peeler. Spread on the cake dough and sprinkle with 25 g sugar.
Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: see manufacturer) for approx. 50 minutes. Let the finished cake rest in the mould for about 10 minutes, then turn out of the mould. Mix jam and 1 tbsp. water and coat the surface of the cake with it.