In a bowl, whisk together 1 part buttermilk with 8 parts of heavy cream. (For example, 1/4 cup buttermilk to 2 cups cream.) Cover the bowl and leave it at room temperature for 12 hours or overnight, until it thickens and separates. Whisk together and transfer to a container; refrigerate, tightly covered.

1/4 cup serving: 187 calories, 19.8g Fat, 1.8g Carbs, 1.3g Protein