1. Peel watermelon and feed into the juicer fitted with a coarse strainer.
2. Pit cherries with a cherry pitter, and put through the juicer fitted with a fine strainer. Initially set the lever to Close, then to Half-Open.
3. Dissolve sugar in watermelon juice to form a syrup, then add cherry juice and pulp. Pour into a metal container, and place in the freezer for a couple of hours.
4. Check the surface, which should start to freeze: stir gently, and put back in the freezer for half an hour.
5. Repeat several times until you achieve the desired consistency.
