Ingredients:

 2lb (900g) Damson plums

1½lb (700g) granulated sugar

½ oz (10g) butter

Clean jam jars

Waxed circles or cling film

Method

•  Wash and halve the plums, removing the stones. If this is too arduous, you can leave the stones in and remove them if they separate when the jam is boiled, or warn people that there may be stones in the finished jam. I like to ensure there are no stones, so I always remove them beforehand.
•  Put three small plates into the freezer – these are for testing whether the jam is set.
• Put the plums into a preserving pan or very large saucepan with a little water and cook on a low to medium heat until the fruit is soft.
• Give the pan a shake from time to time, but only give very gentle stirs, as you want to try very hard not to break up the fruit.
• Either put the sugar into a heat proof bowl and warm it in the oven – along with the clean jam jars (to sterilise them), or use the microwave. Heat the sugar in the microwave for about 3 minutes and the same with the jam jars (NOT the lids as they are metal!). If you use the microwave, you will need to microwave the sugar separately to the jars.
• It is not essential to warm the sugar, but it definitely helps it to dissolve faster when it is added to the plums.
• When the plums are soft, add the sugar to the pan.
• To check if the sugar is dissolved, lift up the spoon and, if there are no little crystals of sugar visible on it, the mixture is ready for boiling.
• Now turn the heat up to its highest setting and as soon as the mixture is up to what old-fashioned cooks used to call a rolling boil, put the timer on for 8 minutes exactly.
• Then, when the 8 minutes are up, remove the mixture from the heat, put a teaspoonful on to one of the chilled plates, allow it to cool, then push the mixture with your little finger. If a crinkly skin has formed on the jam and there is no liquid left, then the preserve is set. If it is not set, boil for a bit longer.
• Allow the jam to settle in the pan for 15 minutes, adding a small piece of butter if there’s any scum, then pour into jars that have been washed, dried and heated in a moderate oven for 5 minutes to sterilise.
• Seal immediately with waxed discs or a double layer of cling film, then cover with the lids.
• When the jam is completely cold, clean and label the jars.