I adore plums which are not as popular here as I would like. There are many varieties but my favourite is the Italian prune plum. It was made to be cooked in some way and I think one of the best ways is into jam.
You will need
1 kg plums (any variety really but make sure they are still firm to the touch)
800 gm sugar
1 tbsp lemon juice
Wash, stone, and cut up the plums. Put in a bowl with the sugar and lemon and let sit in the fridge overnight (stirring once or twice). The next morning, strain the plums and place the juice in a pan. Cook the juice until it has reduced by half or is 221o F (at sea level). Add the plums back in and cook for another few minutes until the plums are heated through and the mixture again returns to 221o F.
In the meantime, you will have washed enough jars in hot, soapy water to hold about a litre of jam. You have also put the jar in the oven for 10 minutes at 250o F. Pour the jam into the jars and let cool.
Put two pods of Star Anise in the plums as they macerate overnight. Make sure you use a whole piece and count them as they are hard to see later. Fish them out after the jam is cooked.
Also, you can take an orange and cut the flesh into small pieces (try to remove all the pith). You add this to the plum mixture with about a tablespoon (45 ml) of finely ground cardamom.