Fill the jar

• Pour the heavy cream into a mason jar, filling it only halfway.
• Add a pinch of salt.

Shake the cream

• Screw the lid on tightly.
• Shake the jar; after about 2 minutes it becomes whipped cream, keep shaking until the butter separates from the buttermilk.

Separate and rinse

• Pour off the buttermilk and keep it for baking.
• Rinse the butter under cold water and press out the remaining liquid.