01 - Combine watermelon cubes, lime juice, and sugar in a blender. Process until completely smooth, ensuring no chunks remain.
02 - Taste the puree and add additional sugar if needed. If using mint, fold in the chopped leaves until evenly distributed.
03 - Transfer mixture to a shallow, freezer-safe baking dish. Spread evenly and place in freezer for 90 minutes.
04 - Remove dish from freezer. Using a fork, scrape the entire surface firmly to break up forming ice crystals into fluffy granules.
05 - Return to freezer. Repeat scraping process every 30 minutes for 3 to 4 hours until mixture reaches light, snowy consistency throughout.
06 - Spoon granita into chilled glasses or bowls. Optionally garnish with fresh mint leaves or lime zest before serving immediately.