Pluck the elderberries from the stems and cook with a little water for 10 minutes. Then press everything through a fine sieve so that only the elderberry juice remains. Put the juice and the pitted plums in a blender or purée briefly with the hand blender so that pieces of the plums can still be seen. Pour into a large saucepan (foams up when boiling), add cinnamon, scrape out the vanilla pod and add the pulp, add the corresponding amount of preserving sugar and cook for 4 minutes. Finally stir in the rum. Fill into clean jam jars, screw on and let stand upside down for 1/2 hour.
Note: Elderberries contain sambunigrin, which can cause diarrhea and vomiting. This substance is destroyed during cooking. Therefore it is essential to adhere to the cooking time!