Sweet Cultured Butter and True Buttermilk

Ingredients

• 4 cups heavy cream
• 1/4 cup buttermilk

Directions

1. Combine the cream and buttermilk in a large bowl, stirring until blended. Drape a kitchen towel over the top without sealing it tightly, then set the bowl in a warm place on the counter. Leave it alone at room temperature for 18 to 24 hours, stopping when the flavor has turned nicely tangy.
2. Move the bowl into the refrigerator and chill the cream for about 2 hours.
3. Using the paddle attachment on a stand mixer, beat the chilled cream hard for 8 to 10 minutes. It will pass through the soft-peak and firm-peak stages before it breaks, separating into little pieces of butter and a thin, watery buttermilk. Beat a bit longer, another 3 to 6 minutes, until the butter gathers into bigger clumps.
4. Set a fine-mesh sieve over a bowl and line it with a double layer of cheesecloth or a single layer of butter muslin. Tip the butter clumps and cloudy buttermilk into the lined sieve and let them drain. Transfer the buttermilk to a jar, cover it, and refrigerate; it should stay usable for about a month.
5. Lift the butter out of the sieve and place it in the bowl that had been catching the buttermilk. Pour in 2 cups cold water, put the bowl in the refrigerator, and chill until the butter firms up, 5 to 10 minutes.
6. Take the butter out of the refrigerator and pour away the water. With the back of a wooden spoon or a butter paddle, press and knead the butter over and over to force out any remaining water or buttermilk. Once the butter is smooth, waxy, and releases no additional water under pressure, enclose it snugly in parchment paper, then wrap it in foil so it is sealed against oxidation. Refrigerate the butter; it should last for up to 2 months, or up to a year when frozen.