Dissolve sugar in water to make a simple syrup. Add watermelon purée. Freeze in an ice cream maker using the manufacturer’s instructions.
You might need to tweak the syrup-to-puree ratio. To check for the correct ratio, drop a clean whole egg into the mix. The portion of the egg that rises out of the mixture should be the size of a quarter. Adjust the water to mixture ratio to make the egg rise or drop in the mix.
Yield: 6 one-cup servings