For the marble muffins, cream margarine with sugar, vanilla sugar. Then add the eggs one by one and finally the milk.
Mix the flour with the baking powder into the mixture. Divide the dough between two bowls. Add the cocoa powder to one half of the batter. Grease muffin tin or line with ramekins.
Pour the light and dark mixture alternately into the mold, using a small fork to gently mix the two doughs with one at the end.
Bake the muffins at 180 °C top/bottom heat for approx. 25 – 30 minutes.