Pour cold heavy cream into a clean jar, bowl, or churn
Let the cream warm slightly to about room temperature
Add a pinch of salt if desired
Shake, stir, or churn the cream continuously
Watch for whipped cream to form first
Keep going until the fat separates from the liquid
Drain off the buttermilk
Gather the butter solids together
Rinse the butter under cold water
Press or knead out any remaining liquid
Shape the butter as desired
Store the butter in the refrigerator