Bring 650 ml of milk to the boil in a saucepan. Stir 150 ml milk, pudding powder and 2 tablespoons sugar until smooth. Remove the milk from the heat, stir in the pudding powder and boil again while stirring for about 1 minute.
Place the pudding in a bowl and place cling film directly on top of the hot pudding. Let it cool down. For the crumbles, heat 200 g butter in a saucepan. Mix 275 g flour, 150 g sugar and 1 packet of vanilla sugar in a bowl.
Add hot fat at once and knead crumbly with the dough hooks of the hand mixer. Finally sprinkle 25 g flour over the crumbles, shake again and let cool. Wash, peel and halve the apple and cut out the core.
Cut the apple halves into thick slices and place them in lemon water. For the sponge mixture, whisk 180 g butter, 100 g sugar, 2 sachets vanilla sugar, lemon zest and salt until creamy.
Add 3 eggs one after the other, alternating with a tablespoon of flour. Mix 250 g flour and baking powder, stir in briefly. Spread the dough evenly on a greased, flour-strewn fat pan (37 x 32 cm) (dough is very firm; it should be!).
Cover the dough in flakes with well drained apple slices. Stir the pudding briefly with the whisk of the hand mixer. Stir in poppy seed mixture and 6 eggs with a mixing spoon. Spread the poppy seed pudding cream on the apples and sprinkle with the crumbles.
Bake in the preheated oven on the middle shelf (electric oven: 175 °C/ convection oven: 150 °C/ gas: level 2) for about 1 hour. Let the finished cake cool down in the fat pan on a grid. Serve with whipped cream.