Put all the ingredients in a large saucepan. Cook for about 10 minutes, stirring constantly. Then puree the mass with a hand blender.
In the meantime, preheat the oven to 150 ° C (top / bottom heat). Then fill the plum sauce in a pan and let it thicken in the oven at 150 ° C for 4 - 6 hours. Stirring occasionally!
The Powidl is ready when it can be spread hot and is black-brown in color. Immediately, very hot, pour into well-cleaned glasses. Be careful that there is no air lock. Put a teaspoon of rum in each glass on top of the sauce and seal the glasses airtight.