Pour the heavy cream into the food processor fitted with the metal blade.
Process in 30-second bursts using the dough button or high speed.
After several rounds, the cream will reach the whipped cream stage.
Continue processing until the cream breaks and the buttermilk separates.
Pour the mixture through a fine mesh sieve into a large bowl, saving the buttermilk for later use.
Rinse the butter under cold water or ice water, pressing out excess liquid until the water runs clear.
Add salt if desired.
Shape the butter and store it in a butter dish, airtight container, or wrapped in parchment paper.