Sterilize 2 glass jars and lids or as many as you'll need to hold 2 cups of cream. Either pop them in the dishwasher on a hot setting or in the oven (100C / 212F) for 10 minutes. If I'm feeling lazy I either skip the sterilizing or just rinse the jars with boiling water from the kettle but sometimes the sour cream ends up being gassy.

Rinse a clean stainless steel saucepan or pyrex jug with boiling water.

Place cream in saucepan or jug and heat gently to 25C (77F). If you're using a pyrex jug and pop the it in a saucepan of hot water to heat. I do this because my pots are cast iron and I don't want the cream to be contaminated by the iron.

Remove from the heat, stir in yoghurt. Pour cream into your 'sterilized' jars and seal with the lids.

Place filled jars in a cooler bag. Fill another 1-2 jars with boiling water and pop them in the cooler bag to to keep everything warm (if it's super hot where you are no need for this).

Stand for 12-24 hours or until the cream has thickened. Don't share or stir as this will cause the gel to break and the cream to be runny.

Refrigerate and enjoy! Depending on your level of sterilization will keep in the fridge for a few weeks to a month.