How to Make It
Place plums, sugar, water, and vanilla bean in a saucepan over medium, and cook, stirring occasionally, until the plums are soft, 5 to 8 minutes. Remove pan from heat, and let plums cool to room temperature. Remove vanilla bean, and discard, or rinse and reserve for another use.
Process plum mixture, cream, and lemon juice in a blender until almost smooth. (There should be some pieces of plum throughout the ice cream.) Chill overnight.
Place chilled mixture in a freezer container of a 1-quart electric ice-cream maker, and freeze according to the manufacturer's instructions. Transfer to an airtight container, and freeze until firm but still scoopable, at least 4 hours.
Nectarine Ice Cream: Substitute 1 lb. nectarines for the Italian prune plums. In Step 1, decrease cooking time to 3 to 5 minutes. Add 1/2 teaspoon of lemon zest to blender in Step
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