For the Heavy Choco Muffins, coarsely chop the chocolate coating, melt it with the butter and the oil over a water bath and then let it cool down a bit.
Sift the flour into a bowl with the cocoa powder and baking powder. Beat the eggs with the sugar in another bowl until nice and fluffy and creamy. The mixture should become light due to the stirring (takes a little time). Then briefly mix the sour cream and water into the egg mixture and add the cooled chocolate-fat mixture.
Last but not least, mix in the dry ingredients (flour, cocoa and baking powder). It’s best to do this on the lowest speed of the hand mixer and add the flour only in batches (otherwise it will dust way too much).
Divide the muffin batter among 12 cups (fill them all about 2/3 full) and bake the Heavy Choco Muffins in a preheated oven at 180 °C top and bottom heat for about 35 minutes.