Homemade Yogurt-Churned Butter

Fill a tightly sealed jar or churn no more than two-thirds full, then begin shaking at a steady pace. For the first 10 minutes, you will see only foam; that is normal. When yellowish grains appear on the surface and the sound becomes more solid, the butter is separating. Keep going until the grains are about the size of chickpeas. If the mixture warms up, refrigerate it for 10 minutes, then continue.

Pour the contents into a cheesecloth-lined strainer and collect the buttermilk in a separate bowl; drink it rather than discarding it. Squeeze the butter grains left in the cheesecloth together by hand to form one lump.

Put the lump in a wide bowl of ice water and knead it by pressing with the back of a spoon. Pour off the cloudy water and repeat with fresh ice water. Wash it three or four times, until the water runs clear; leftover buttermilk inside will make the butter turn sour within 2 days. Finally, work in the salt, wrap the butter in parchment paper, and refrigerate.