Place cubed Watermelon on a Baking Sheet lined with Non-Stick Aluminum Foil.
Chill for 3-4 hours or until completely frozen.
When the Watermelon is frozen and ready to use, create a concentrated simple syrup in a small Glass Measuring Cup by bringing Water to a boil.
Add Sugar and 1 1/2 teaspoons Lemon Juice. Mix until dissolved.
Add frozen Watermelon to Food Processor (Note: don’t overpack it…you can always add more or make it in a couple of batches.)
Pour in about 2 Tablespoons of hot Simple Syrup and begin processing. Continue to add Simple Syrup until you get to desired sweetness and consistency. (Note: if you reach the level of sweetness that you want but it is not quite smooth enough, add hot water until smooth.)