Preheat the oven to 200 ° C and fill a 12-cup muffin tray with paper cases or - if no muffin tray is available - always place 2 tins one inside the other on a baking sheet.
Roughly chop the chocolate with a knife. Then mix the flour, cocoa and baking powder, cinnamon, sugar and the chopped chocolate well in a bowl.
In a small bowl, whisk the eggs with a fork, then stir in the oil until everything is well mixed. Finally stir in the milk.
Now add the liquid to the flour mixture and stir only briefly (preferably with a fork or similar) so that the dough is just mixed. Too long stirring quickly makes the dough tough.
Pour the batter into the molds and bake in the oven for 20 minutes. The muffins are ready when they still give a little under pressure. Take the muffins out of the mold, let them cool completely on a wire rack and decorate with melted chocolate and sweets if you like.