Crumble the chocolate and melt slowly in a water bath, then set aside. Butter and flour a cake pan. Preheat the oven to 180°C top/bottom heat (convection oven: 160°C).
Cream the butter and add the sugar. Now add the salt. Gradually add the eggs and mix until the sugar has dissolved. The mixture should be nice and fluffy and light. Sift flour, cornstarch and baking powder over the mixture and stir in. Divide the batter into 2 halves.
For the orange part, grate the orange and squeeze it (about 80-100 ml of juice). Now add the grated zest and juice. Then pour the batter into the prepared cake pan.
For the chocolate part of the 2nd half of the dough, add the melted and slightly cooled chocolate, cocoa powder, rum flavoring and milk. Mix everything well. Now pour this dark batter on top of the light batter and smooth it out. Put into the hot oven and bake on the middle shelf for about 60 minutes.
Then let cool in the pan for another 10 minutes. Then turn out and let cool.
Either brush with melted cake glaze or dust with powdered sugar.
The cake should still be nice and moist after cooling and the chocolate part should be a little moist – but not raw.
My tip: The truffle flavor of the chocolate part depends on the chocolate used in this cake. I usually take a bar of dark milk and a dark chocolate with chocolate mousse – filling.
