Combine all ingredients in medium saucepan and bring to a gentle boil over medium-high heat. Cook, stirring often, until the sugar dissolves and the mixture is smooth, 1 to 2 minutes.
Transfer to a bowl, cool to room temperature, and then cover and chill until very cold.
Transfer to the bowl of an ice-cream maker and freeze according to manufacturer's directions.
Serve at once, or transfer to an airtight container and freeze for up to 2 weeks.