This frozen treat will make your insides feel like the temperature is taking a plunge, but your heart will be warm at the thought of a taste of Buttermilk-Plum Ice Cream. Its ruby-colored swirls—the source of its name come from fresh plums. Half-and-half, buttermilk, and heavy cream help form its rich base, while peeled and chopped black plums add in beautiful color and flavor.
Bring blueberries, 2 Tbsp. sugar, and water to a boil in a small saucepan over medium heat; reduce heat to low, and simmer 10 minutes, stirring often. Cool 30 minutes; cover and chill 2 to 3 hours.
Whisk together condensed milk and next 5 ingredients; cover and chill 2 hours.
Pour milk mixture into freezer container of a 1-qt. electric ice-cream maker, and freeze according to manufacturer's instructions. (Instructions and times will vary.)
Remove container with ice cream from ice-cream maker, and freeze 30 minutes.
Stir lemon zest into prepared ice-cream mixture, and swirl in chilled blueberry mixture. Transfer mixture to an airtight container or a loaf pan covered tightly with aluminum foil; freeze 3 to 4 hours or until firm.