01 - Place watermelon cubes into blender. Add fresh lime juice and granulated sugar. Blend on high speed until completely smooth and no chunks remain.
02 - Taste mixture and add additional sugar if preferred. If using mint, stir chopped leaves into blended mixture until evenly distributed.
03 - Pour blended mixture into shallow freezer-safe baking dish. Spread evenly across surface using spatula for uniform freezing.
04 - Place dish in freezer for approximately 90 minutes. Remove and use fork to scrape surface thoroughly, breaking up ice crystals that have formed.
05 - Return dish to freezer. Every 30 minutes, remove and scrape entire surface with fork. Repeat this process for 3 to 4 hours until mixture becomes light, fluffy, and grainy throughout.
06 - Scoop granita into pre-chilled glasses or bowls. Optionally garnish with fresh mint sprigs or grated lime zest before serving immediately.