Preheat the electric stove: 175 ° C top / bottom heat, fan-assisted air: 150 ° C. Line a box shape with parchment paper.
Melt the chocolate and butter in a hot water bath. Allow to cool slightly. Mix the flour, brown sugar, vanilla sugar, baking powder, a pinch of salt and cocoa together.
Beat the eggs with the whisk of the mixer for approx. 3 - 4 minutes until frothy. Gradually stir in the cooled but still liquid chocolate butter. Add flour mixture, mulled wine and rum and stir in briefly.
Pour the dough into the mold and smooth it out. Bake in the preheated oven for 50 - 55 minutes (make a stick test). Let the cake cool down a little in the tin, then carefully place it on a wire rack.
For the topping, melt the cream, coconut oil and white chocolate, stir and allow to cool. Pour over the cake and let a little run down the sides.