Crumble amarettini or coarsely grind with the blender.
Rinse and dry plums, halve and pit, dice.
Combine amarettini (up to 3 tablespoons) with flour, cinnamon and baking soda. Add plums.
Combine yogurt, quark, eggs and oil, mix until smooth. Stir in flour mixture quickly. Pour batter into lined with paper muffin cups muffin pan. Bake in preheated oven at 180°C (approximately 350°F) for about 25-30 minutes. Allow to cool slightly, remove from muffin pan and cool completely. Serve.