The Preparation
Let cream come to ~65°F before starting. Not cold, not warm.
Pour cream into stand mixer with whisk attachment. Beat on medium.
Watch the stages: whipped cream (3 min), stiff peaks (5 min), grainy/over-whipped (7 min), then butter separates from buttermilk (10-15 min total).
Stop immediately when butter clumps and buttermilk splashes in the bowl.
Pour off buttermilk and save it.
Transfer butter to a bowl of ice water. Knead to flush out residual buttermilk. Change water and repeat until water runs clear.
Press out excess water. Add salt to taste. Fold in. **Note:** Save the buttermilk. Use it for pancakes, biscuits, or salad dressing.
The Chef's Notes
Higher fat cream means better yield and a richer flavor. The phase inversion — cream going from oil-in-water to water-in-oil — happens suddenly. Do not stop the mixer the moment it looks broken.