Stir 200 ml milk, 100 g sugar and pudding powder until smooth. Boil up the rest of the milk. Remove milk from the heat and stir in the pudding powder. Let simmer for about 1 minute while stirring. Pour the pudding into a bowl.
Cover the surface with foil, let it cool down, then put it in a cool place.
Cut the butter into pieces. Knead 250 g sugar, flour, butter, 1 egg and cocoa powder first with the dough hooks of the hand mixer, then with your hands to crumbles. Spread approx. 2/3 of the crumbles as a base on a greased and floured fat pan of the oven and press them down.
Wash apples, grate dry. Remove the core with an apple corer. Cut apples into rings, sprinkle with lemon juice.
Pour about half of the pudding into a bowl. Stir in 2 eggs, poppy seed mixture and Calvados. Spread the poppy seed pudding on the bottom. Mix the remaining pudding with 2 eggs and spread on the poppy seed pudding.
Cover with apple slices, spread the remaining crumbles on top. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: see manufacturer) for approx. 1 hour, remove from oven and let cool on a cake rack.
Chop white chocolate and melt it over a warm water bath. Decorate cake with liquid chocolate. Leave to cool. Serve with whipped cream refined with poppy seeds.