Whip 1 pint heavy cream with a stand mixer fitted with whisk attachment. Be sure to cover mixer and bowl with a clean kitchen towel, or risk a splattering mess. The cream will go through several stages -- foamy, then frothy, then soft peaks, stiff peaks, and, eventually, butter. It will take anywhere from 6 to 15 minutes until the butter separates from the buttermilk and starts to spatter.

Pour buttermilk into an airtight container and refrigerate; it will keep for 3 days.

Form butter into a ball. Working over a colander in the sink, rinse butter under cold running water to remove any remaining buttermilk. If butter is too soft, float it in a bowl of ice water for 20 minutes, then continue. When water runs clear from butter in your hands, knead butter firmly to remove all moisture.

Butter will stay fresh longer if it's salted, so work 1/4 teaspoon kosher or sea salt into butter. Wrap in wax or cheese paper, or pack into ramekins.