For the eggnog coconut marble cake, first preheat the oven to 150 degrees top and bottom heat. Beat the eggs with the icing sugar and vanilla sugar for about 3 minutes until foamy. Stir in flour, coconut flakes and baking powder and slowly add the egg liqueur and oil and continue to stir for a minute.
Grease gugelhupfform with margarine and sprinkle with coconut flakes. Pour in 2/3 of the batter. Stir into the remaining batter the melted cooking chocolate (2 tablespoons of cocoa will work as a substitute) and 1 tablespoon of rum and pour into the mold as well. Marble the eggnog coconut marble cake with a knitting needle. Bake at 150 degrees for 1 hour.