Wash and stone the plums and cut into small pieces. Mix the flour, baking powder, salt and sugar in a large mixing bowl. Whisk eggs, oil, yogurt, orange peel and 5 tablespoons of orange juice and stir briefly into the flour with a spoon until everything is just mixed. The dough should not be pliable. Fold in the plums. Place paper sleeves in the 12 hollows of a muffin tin or grease them. Pour in the dough and bake in a preheated oven (electric stove: 175 ° C / convection: 150 ° C) for 25-30 minutes until golden brown. Let cool on a wire rack.