To make 5 average sized jars:
1.5 kilos plums, washed, halved and stoned
1.25 kg granulated sugar
2 heaped tsp ground cinnamon
1. Place the halved and de-stoned plums together with the water in a very large pan, preferably a jam or maslin pan. Place on a medium heat and simmer for 10 to 20 minutes until the fruit and skins are a little softened.
2. Stir in the sugar and cinnamon and raise the heat. Bring to a simmer and allow to boil reasonably furiously until setting point is reached, either by a thermometer temperature of 104.5 or by testing a drop on a cold saucer (place a couple in the fridge at the start of the jam making process). If you can wrinkle the jam (just a little) after a minute on the saucer it’s good to go.
3. Immediately pour into sterilised jars and top with a wax disc and the jar lid whilst still piping hot.