In a large bowl, whisk together all the ingredients. Taste and adjust sweetness to your liking.
Place the mixture into the ice cream maker. Churn 15 minutes. It should look slushy.
Either serve the frozen lemonade in glasses now, or transfer to a container and freeze for an hour. If it is still slushy, simply let it chill in the freezer for an additional half hour, then stir again. Repeat until it has a sorbet texture. Serve with an ice cream scoop.