Cream fat, sugar, vanillin sugar and salt with the whisk of the hand mixer. Add the eggs bit by bit. Melt the chocolate coating in a hot water bath. Fill a good 1 tablespoon into a small freezer bag for later decoration, set aside.
Add the remaining chocolate coating to the dough. Mix flour, cocoa, baking powder and hazelnuts and stir in by the spoonful. Finally add the cream. Fill the dough into a greased square baking tin (26 x 26 cm; or into a round fruit cake tin with 30 cm Ø).
Bake in the preheated oven (electric oven: 175 °C/ gas: level 2) for approx. 45 minutes. Let rest for 10 minutes. Then turn out onto a cake rack and let it cool down. Pour the milk into a high mixing bowl.
Add cream powder and stir with the whisks of the hand mixer at highest speed for about 3 minutes. Warm up the jam in a small pot, possibly passing it through a sieve. Spread 2/3 of the jam on the bottom.
Fill with cream and smooth the surface. Chill the cake for about 1 hour. Drain the apricots well on a sieve. Collect the juice and use it for other purposes. Briefly reheat the chocolate coating in the bag in a cup of hot water.
Cover the cake with apricot halves. Spread the fruit with the rest of the jam. Cut off a small tip of the freezer bag. Pull the chocolate coating in strips over the cake. Decorate with lemon balm as desired.