Combine the granulated sugar and water in a small saucepan over medium heat. Stir until the sugar is completely dissolved, about 2 to 3 minutes. Do not let it boil. Remove from heat and allow the simple syrup to cool to room temperature before using — about 10 to 15 minutes, or speed this up by placing the pan in an ice bath.

Add the cubed watermelon to a blender and blend on high until completely smooth and liquid, about 30 to 45 seconds. If using fresh mint leaves for the mint variation, add them to the blender now and blend until fully incorporated.

Add the cooled simple syrup, fresh lime juice, lime zest, and pinch of sea salt to the blender. Pulse briefly to combine everything thoroughly, about 10 seconds. Taste the mixture and adjust sweetness or lime juice as desired — it should taste bold, bright, and slightly sweeter than you want the final result, since freezing will mute the sweetness slightly.

Optional: For a more refined texture, pour the blended mixture through a fine-mesh strainer into a large bowl or measuring cup, pressing gently with a spatula to extract all the liquid. Discard the remaining fiber. Skip this step for a more rustic result.

Pour the watermelon mixture into a wide, shallow 9x13-inch metal baking pan — metal conducts cold more efficiently than glass and will speed up the freezing process. Spread it into an even layer. Place the pan in the freezer, uncovered, on a flat surface.

Freeze for 45 minutes to 1 hour, until the edges and bottom of the mixture begin to freeze and look slushy and opaque while the center remains liquid.

Using a sturdy dinner fork, scrape the frozen edges and bottom of the pan toward the center, breaking up any ice crystals that have formed. Drag the fork in long strokes across the entire surface to create light, feathery shards. Return the pan to the freezer.

Repeat the scraping process every 30 to 45 minutes for a total of 3 to 4 scraping sessions over approximately 3 to 4 hours. With each session, the granita will become increasingly crystalline, airy, and textured. The final result should be a loose, fluffy pile of bright pink-red ice crystals — not a solid block and not a slushy liquid.

Chill your serving glasses or bowls in the freezer for 10 minutes before plating for maximum presentation impact. Fluff the granita one final time with the fork, then scoop generous mounds into the chilled glasses.

Garnish each serving with a sprig of fresh mint, a wheel or wedge of lime, and optionally a small dollop of lightly whipped cream or coconut cream. Serve immediately for the best texture, as granita softens quickly at room temperature.