Line the recesses of a muffin tray (for 12 pieces) with paper baking cups. Drain the cherries. Chop chocolate. Mix flour, baking powder and sugar in a bowl. Whisk egg, buttermilk and oil.
Add flour mixture and mix everything briefly. Add cherries and 75 g chopped chocolate to the dough.
Spread the dough into the hollows. Bake in the preheated oven (electric oven: 175 °C/circulating air: 150 °C/gas: see manufacturer) for 20-25 minutes. Cool down.
Melt the rest of the chocolate in a hot water bath. Pour into a freezer bag, cut off a small corner at the bottom and decorate the muffins with it in thin strips. Let the chocolate dry.