Wash the plums and blackberries, stone the plums. Peel and core the apple and cut into small pieces. Put everything in a tall container and puree with the hand blender. Then put in a saucepan with the preserving sugar, bring to the boil and boil for 3 minutes. Pour hot into clean glasses, screw on and turn upside down. After approx. 20 to 30 minutes you can turn the glasses over again and let them cool down.