1/3 cup sugar
1/4 cup water
1/3 cup light corn syrup
2 cups pureed watermelon
1 tablespoon lemon juice
Combine sugar, water and syrup in a saucepan. Stir until it boils. Reduce heat and simmer for 5 minutes. Let cool. Refrigerate.
Remove meat from the watermelon and discard seeds. Puree in a blender. Measure and add 3 cups of watermelon and lemon juice to the cold sugar, water, syrup mixture.
Freeze the mixture in an ice cream machine for 20 to 30 minutes, according to the manufacturer's instructions.