Stir together all ingredients in medium bowl until sugar has dissolved. Pour into large loaf pan (or other pan of similar size); cover and freeze for 8 hours. Remove from freezer and scrape surface with fork until it is icy and has a crystalline texture throughout. Return to freezer and freeze for at least 4 hours more; scrape again with a fork.
Spoon into small cups or glasses and serve immediately. May be made several days ahead and stored tightly covered in the freezer until ready to serve.