Mix the margarine, sugar and vanilla sugar until foamy, add the egg and yoghurt and whisk briefly. Mix the flour and baking powder and sieve in and stir in until the dry ingredients are moist.
Roughly chop the chocolate, drain the morello cherries and collect the juice. Fold the chocolate and cherries into the mixture and add sweetener to taste.
Pour the dough into a silicone muffin pan and bake in the preheated oven on the middle rack at 180 degrees (gas: level 3) for about 30 minutes.
Mix the cherry juice with powdered sugar and decorate the cooled muffins with it.