Pour the cold heavy cream into a large mixing bowl or stand mixer.
Beat on medium-high speed for about 8–12 minutes. The cream will first turn into whipped cream, then begin to separate.
Continue mixing until the butter solids separate from the liquid (buttermilk).
Strain the mixture using a fine mesh sieve or cheesecloth to separate the butter from the buttermilk.
Rinse the butter under cold water while gently pressing it to remove any remaining liquid.
Add salt if desired and mix until fully combined.
Shape the butter and store in an airtight container in the refrigerator.
Do not skip rinsing the butter — this helps it last longer and improves flavor.
The leftover liquid is buttermilk and can be saved for baking.
