Make Ahead Tip: Freeze in an airtight container for up to 1 week. Let soften slightly before serving.
If using frozen fruit, measure it frozen and then thaw before pureeing.
If you don't have an ice cream maker, freeze the mixture in a shallow metal cake pan or ice cube trays until solid, about 6 hours. Break into chunks and process in a food processor until smooth, stopping to scrape down the sides as needed.