Whisk 1 quart buttermilk, 1 cup sugar, 1/2 cup sour cream and the zest and juice of 1 lemon in a bowl until the sugar dissolves. Refrigerate at least 2 hours. Churn in an ice cream maker according to the manufacturer's instructions. Transfer to an airtight container and freeze until firm, at least 3 hours.
Photograph by Anna Williams