Preheat your oven to 180°C / 356°F

Grease your gugelhupf cake tin with a knob of soft butter and dust it with flour. Set aside.

In a large bowl cream together butter and sugar. Add eggs and mix until everything comes together.

Mix in the flour and the baking powder.

Add the milk, coffee and sour cream.

Pour half the batter into a seperate bowl and add the cocoa powder to it.

Spoon half the light batter into the cake tin and spread it out. Add half the dark batter and carefully swirl through the two layers with a small spoon. Don't overdo it or you won't have a pattern in the end. Repeat with the remaining batter.

Bake the cake for 40-45 minutes or until a wooden toothpick comes out clean.

Remove the cake from the tin and let it cool.

In a bain marie very slowly melt 2/3 of the dark chocolate. When it's melted, take it out of the bain marie and stir in the remaining 1/3 of the dark chocolate. Stir until it's melted and pour it over the cake immediately.

Roughly chop the white chocolate and sprinkle it over the top of the glaze.