Mix the cream and yoghurt together in a bowl, cover with a clean cloth and leave at room temperature for 24–36 hours, until thickened and pleasantly sour.
Chill for at least 4–5 hours, preferably overnight, then churn using a stand mixer, hand churn, whisk or even a spoon until the butter separates from the buttermilk.
Drain the buttermilk and save it, it’s excellent in pancakes, baking and marinades.
Wash the butter thoroughly in ice-cold water, kneading and changing the water until it runs clear.
Salt to taste, shape and wrap in greaseproof paper.
Keep refrigerated, or freeze for longer storage.
