Directions

1. Step 1 Pour the cream into a jar with a clean marble inside. Screw the lid on tightly. Shake the jar continuously for 5 mins (you can take turns shaking with someone else). The movement of the marble acts as a whisk and helps the butter to churn. You can do it without the marble, it just takes longer. At first the cream will thicken to whipped cream, then it will get even thicker. After about 5 mins you will hear sloshing in the jar - give it a few more vigorous shakes, and that's the butter churned.
2. Step 2 Scrape out the contents into a sieve sitting over a bowl - the liquid that drains out is buttermilk (which can be kept and used for baking or in pancakes), and the fatty solid in the sieve is the butter.
3. Step 3 With clean hands, squeeze the butter between your fingers over the sieve to squeeze out any more buttermilk, while working it into a ball. 'Wash' the butter in a bowl of ice-cold water to get rid of any residual buttermilk. Beat in a small pinch of salt. Will keep in the fridge for up to one week.