I always stone the plums first, then for every pound of fruit, you will need a pound of sugar. Put the plums in a large pan with a splash of water and bring to the boil. Turn the heat down and leave on a rolling simmer for a good 30 minutes until the fruit is really tender and the liquid is reduced. Add the sugar and stir constantly until it is all dissolved then bring up to a rolling boil. Boil, stirring carefully occassionally, for about 5 to 10 minutes, by which time it should have reached setting point. If you do not have a sugar thermometer then test for a set by placing a couple of saucers in the freezer an hour before you start jamming, then take the pan off the heat, take a teaspoon full of the jam and dollop it onto the freezing cold saucer. Leave for a couple of mins and then poke it with your finger. If a wrinkled skin forms, you should have a set. If it is still fluid and runny, place the pan back on the heat, get up to a rolling boil, and boil for another 5 mins, then repeat the test. Once you have a set, pour CAREFULLY into warm, sterile jam jars and seal immediately. When cold, label and store in a cool dark place. YUM! Love plum jam. I added a drop of sloe gin to some of my plum jam this time, for a little extra grown up flavour. If you wanna add some booze, pour it into the jamjar before adding the jam, then fill as before!
