Very straightforward of jam methods, producing a softly set preserve that will keep in a jar for a couple of weeks in the fridge. To make a jam that will last longer, you will need to boil for a little longer so that it sets more firmly. Including some of the fruit's stones is not necessary, but it can add a faint almond note to the finished jam. 

Ingredients to make about 4 x 400g jars:

1.5kg plums 
1.4kg sugar 
250ml water 

Method:

Rinse the plums, removing any stray leaves, stalks and twigs as you go. Halve them and remove the stones. Crack six or so of the stones with a hammer and discard the rest.

Tip the fruit, sugar, water and reserved stones into a deep, stainless steel saucepan and bring to the boil. (You will find the water only partially covers the fruit.) Turn the heat down so that the fruit simmers to partial tenderness. You can expect this to take about 30-40 minutes, depending on the ripeness of your plums.

To test if the jam is set, put a little on a cold saucer and place in the fridge for five minutes. Run your finger through the jam on the saucer. If it has formed a thin skin, it is ready to pour into jars.

Scrape off any froth with a draining spoon, lifting out the stones that have risen to the surface. Ladle the jam into warm, sterilised jars and seal.