Prepare the jars
Preheat the oven to gas 1, 140°C, fan 120°C. Sterilise 4 x 350ml (12fl oz) jam jars and lids by lowering them into a pan of boiling water; leave for 1-2 minutes. Using tongs, carefully lift out. Place the jars in the oven to dry. Once completely dry, remove and set to one side to cool.
Put 2 saucers in the freezer (for testing the consistency of the jam). Cut out 4 circles of greaseproof paper to fit the jar tops and set aside until needed.