Finely chop white and dark chocolate and melt 100 g each separately over a hot water bath. Set the rest of the chocolate aside separately. Let the melted chocolate cool down.
Cream fat, sugar, salt and vanillin sugar for about 10 minutes. Stir in the eggs one by one. Add crème fraîche and mix. Mix flour and baking powder and stir in briefly. Grease a ring cake tin (2 litres capacity) and dust with breadcrumbs.
Mix half of the dough with the white chocolate and fill into the mould. Mix the remaining dough with the dark chocolate. Spread the dark dough on the light dough and marble with a fork.
Bake the cake in a preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for about 1 hour. Remove, let cool for 5 minutes and turn out onto a cake rack. Let cool off. Melt the rest of the chocolate separately over a hot water bath and spread on the cake with a spoon.
Let the chocolate dry and decorate the cake with chocolate hearts.