Pour the cream in a big kitchen bowl, and whisk it with a hand mixer on medium speed. Continue to whisk until the butter starts to separate. It will take some time, so don't lose your patience.

Pour off the buttermilk. Rinse the butter by pouring ice water over it and pressing the remaining buttermilk out with a small spatula or a spoon. You can also knead it by hand if you can stand the cold water. When the water starts to go "milky" it's time to pour it off and add some new. Continue like this until the water is completely clear and all buttermilk is pressed out from the butter.

Add salt and work it trough the butter.