In an enameled dutch oven on low heat cook the plums until they are soft stirring often. Plums easily burn so stay attentive. Once the plum are softened using a potato masher break down the plums until only small bits are left.
Add the sugar and balsamic bring the mixture up to a boil, stirring constantly. Once the mixture is boiling add the pectin, return to a boil for one minute.
Ladle the recipe into the jars leaving 1/4" headspace. Process in water bath at a full boil for 10 minutes.
Yields 3 half pints.
I really enjoyed the original strawberry balsamic and thought about the combination with the plums and whether it would be interesting since the sweetness of the balsamic adds some depth to the jam flavor.