Add the plums, sugar and salt into a saucepan stirring to combine. Bringing the stove to medium high, bring the mixture to a boil and continue heating until the sugar dissolves. During this process, use a utensil similar to a potato masher to mash the plums, breaking them down.

Add lemon juice and stir to combine.

Lower the heat to a simmer and keep stirring while boiling, skimming off any foam.

Continue stirring for about 20 minutes total. You’ll know that the jam is ready when the juices have thickened significantly. You can also test whether your jam is ready by using a cold plate! To do this, add a small plate to the freezer and place a spoonful of jam on the plate. If your jam sets within one minute on the cold plate you’re finished! If not, you’ll need to continue cooking a bit longer.

Allow to cool completely before using in your mascarpone plum buttercream.