Pop 5-6 jars in the dishwasher to sterilise.

Wash fruit and chop into halves or quarters and discard stones.

Layer fruit and sugar in a large pot. Place on a high heat and squash the fruit to help release the juices.

Add lemon juice and bring to the boil. Place a small plate in the freezer.

Boil for 1 1/2 – 3 hours.

To test for setting, place about 1 teaspoon of jam on the small plate and return to the freezer for 3-4 minutes. Push jam with your finger, if it seems firm enough, you’re done. If not keep cooking and testing.

Stir butter in. Divide hot jam between warm jars straight from the dishwasher. Seal immediately.