If you've got excess plums, a good way of using them up is to make Powidła - a Polish plum spread. You need a fair bit of plums to get a decent quantity, as you drive off the moisture to help thicken it.
Really simple to make, but requires a bit of time. And watching the pot, stirring regularly to prevent catching.
Wash, halve and stone as many plums as you want to use. Weigh. Then weigh out half the amount of sugar and set aside.
Cook the plums till very soft (you might need to add a splash of water at the beginning), then add the sugar, stir till dissolved, and then cook on a very low heat until very thick and gloppy.
This last stage takes a fair few hours - the beauty of it is, unlike jam, you can turn it off, pop a lid on, and leave it until you've time to have another session. When you can leave a clear channel at the bottom of the pot with a wooden spoon, ladle into clean jars and seal while hot.
This is lovely on hot buttered toast.