1.8kg/4lb damsons, washed
30g/1oz knob of butter
1. Place your jam jars in the oven 150c/300f/GM2/AGA, warming oven.
2. Put 2 saucers in the freezers so they will be cold when you need to check for “the set”.
3. Put the damsons into a preserving pan or large saucepan with the water and bring to the boil. Cook until really soft, mash to release stones.
4. Add the sugar and butter. Bring slowly to the boil, stirring every so often so the sugar dissolves. Boil for 20mins until setting point is reached. Skim off any scum that rises to the surface and remove as many stones as possible.
5. Check for setting pint by spooning a little of the jam on to a cold saucer. Chill in the fridge for a few minutes, then push the jam with your finger. If it wrinkles, it is ready, if not, return it to the pan to boil for another 5-10mins.
6. Pour the jam into warm sterilised jars, cover with wax discs and lids. Cool and label. The jam will keep in a cool, dark place for up to 12 months.