In one quart batches, whip (stand mixer) or blend (blender) cream at a high rate of speed (use a splash guard if available).
After 10-15 minutes, the fat will separate from the whey into yellow globules. Turn off machine.
Line a colander with muslin or a flour sack towel and place over a large bowel.
Pour butter and whey through the cloth lined colander, and repeat steps 1-4 until all cream is processed. Drain until the butter looks relatively "dry".
Twist cloth up into a bundle, squeezing extra whey from the butter, and occasionally rinse the butter bundle under ice cold running water. Continue to squeeze and work the butter until no whey seeps through the cloth.
Transfer worked and rinse butter into a bowl and add a inch of sea salt and combine thoroughly.
Divide butter into four ounce "logs" and wrap in wax or parchment paper. Freeze until use.