Bring the water and the sugar to a boil, whisking to dissolve the sugar. Turn off the heat when the mixture has boiled and add the mint leaves. Let it steep for five minutes. Add the rum, lime juice and salt. Transfer the mixture to a blender and puree on high for about three minutes. Pour the mixture into a shallow pan and freeze overnight.

Scrape with a fork and serve in a chilled glass with rim coated with coarse sugar.

Adjust to taste and flavorings may be changed. Additions of fresh berries give a great summer look and flavor. Garnish with lime slice.