Fit a stand mixer with the whisk attachment or use a large mixing bowl with a hand mixer fitted with a whisk attachment. Ensure your bowl is large enough because the cream will expand as it whips.

Pour the heavy cream into the bowl and whip on medium speed for about 10 minutes. Watch for stiff peaks to form. At this point, add the sea salt if using. Continue whisking until the butterfat separates from the buttermilk.

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

Using your hands or a spatula, 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. Optionally, place the wrapped butter in a resealable plastic bag for additional protection.

Refrigerate the wrapped butter to allow it to firm up. Homemade butter stays fresh in the fridge for up to 3 weeks or can be frozen for up to 9 months.