The greengages for this jam should be very firm and slightly under-ripe. Discard any bruised fruit. This jam keeps well and is particularly good with hot buttered toast.
6 lb. greengages, washed, halved and stoned
1 pint water
6 lb. sugar
In a preserving pan or large saucepan, bring the greengages and water to the boil over high heat. Crack ten of the stones and add the kernels to the pan.
Reduce the heat to moderate and simmer for 20 minutes, or until the greengages are soft. Add the sugar and stir until it has dissolved.
Bring the jam to the boil and boil for about 15 minutes or until setting point is reached.
To test for setting point, remove the pan from the heat and spoon a small amount of the jam on to a saucer. Allow it to cool. If it sets and wrinkles when you push it with your finger, the jam is ready. If not, return the pan to the heat and continue boiling, testing frequently. If you use a sugar thermometer, the jam should register 220°F to 222°F.
When setting point has been reached, remove the pan from the heat. With a slotted spoon, skim off the scum from the surface of the jam.
Pour the jam into clean, dry, warmed jam jars. Seal each jar with a jam cover, label and store in a cool, dry place.