Gather ingredients: heavy cream (or whipping cream)
Pour cream into a bowl or jar
Whisk or shake until it thickens into butter and separates from buttermilk
Stop when butter forms clumps and liquid separates
Strain off the buttermilk
Rinse butter with cold water and squeeze to remove remaining buttermilk
Optional: salt to taste (for salted butter) and mix well
Press butter into a container and cover
Refrigerate and use within about 1–2 weeks, or freeze for longer storage