Put 2 small plates in the freezer before you start.
Sterilise 1 x 500 ml or 2 x 250 ml jars by washing in hot soapy water or take straight from dishwasher, filling with boiling water, emptying and then placing in oven for 20 minutes at 140°C then leave in oven until jam is ready. Washed lids should be sterilised with boiling water and then left to drain.