Coarsely chop the chocolate coating and melt it over a warm water bath. Peel apples, quarter them, remove seeds and cut into large cubes. Sprinkle with lemon juice. Place the fat, salt, 250 g sugar and vanilla sugar in a mixing bowl and whisk until thick and creamy.
Stir in the eggs one by one. Mix flour, sauce powder and baking powder. Alternately stir in with the milk. Halve the dough. Stir cocoa and melted chocolate coating under one half of the dough. Cut the vanilla pod lengthwise, scrape out the pulp and stir into the second dough, then carefully lift the apples.
Place the dough alternately in a well greased, flour-spread springform pan with a tube bottom insert (26 cm Ø). Marble with a fork. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for approx. 50 minutes.
Take the cake out of the oven. After 10 minutes, turn out onto a cake rack and let it cool down. Decorate with icing sugar, lemon balm and possibly with apple slices. Whipped cream tastes good with it.