How to Make It
In a medium bowl, whisk all of the ingredients together until well blended. Cover with plastic wrap and let stand at room temperature for 48 hours, then refrigerate for 24 hours.
In the bowl of a stand mixer fitted with the whisk, beat the cultured cream mixture at low speed until the butter forms and the buttermilk separates out, 8 to 10 minutes. Drain the butter in a cheesecloth-lined sieve; save the whey for another use. Wrap the cheesecloth around the butter and squeeze out all of the excess buttermilk. Transfer the butter to a medium bowl or a jar, cover and refrigerate.