Pour the cream into a suitably sized lidded jar. Add the buttermilk and give a good stir.
Place the lid on the jar and leave to culture at room temperature for approximately twenty four hours. It may take more or less time than this depending on the ambient temperature. It's ready once it's turned thick and tastes pleasantly sour.
Store in the fridge. It will keep well for at least two weeks.
Notes
Make sure your buttermilk is cultured and not pasteurised. It won't work otherwise.If you can't get hold of buttermilk, you can use kefir or yoghurt instead.If the buttermilk starts to separate at any point, just give it a good stir.Please note: calories and other nutritional information are per serving. They’re approximate and will depend on exact ingredients used.