Fit a stand mixer with the whisk attachment or use a large mixing bowl with a hand mixer fitted with a whisk attachment.

Pour the heavy cream into the bowl and whip on medium speed for about 10 minutes until stiff peaks form. Add the sea salt if using and continue whisking until the butterfat separates from the buttermilk.

Set a mesh sieve over a smaller bowl and pour the mixture into the sieve so the butter remains on top and the buttermilk drains through.

Squeeze the butter to remove as much buttermilk as possible. Dip the butter into ice water and squeeze again to rinse and remove residual buttermilk.

Transfer the butter to parchment or wax paper and shape it into a log or block. Wrap tightly and secure with kitchen twine or ties.

Refrigerate the wrapped butter to allow it to firm up.