Preheat the oven to 180 ° C and line the muffin tray with paper liners, as the muffins are very juicy and otherwise difficult to get out of the mold.
Coarsely grate the chocolate. Peel and coarsely grate the zucchini.
Beat the butter, sugar, eggs, oil, yogurt and vanilla sugar until frothy. Add flour, cocoa powder, baking powder, baking soda, cinnamon, allspice, zucchini and chocolate and stir in. Pour the batter into the molds. Put in the oven and bake for 20-25 minutes.