Before you start, sterilise the jars by washing them in hot soapy water (or take them straight from the dishwasher). Fill with boiling water, empty, and then place in the oven for 20 minutes at 140°C, 120°C fan, 285°F, gas mark 1, where you leave them until the curd is ready. Washed metal lids should be sterilised with boiling water and then left to drain (if still wet, place in oven once you’ve turned the heat off and run with just the fan for a few minutes to dry off).