Watermelon granita is a refreshing Italian-style frozen dessert that captures the pure essence of summer. This simple treat combines sweet watermelon puree with a quick homemade lime syrup for a bright, citrusy finish. It requires no special ice cream maker, relying instead on a simple freeze-and-scrape method to build its signature icy texture. Serve this cooling slush in chilled cups on a hot afternoon or as a light palate cleanser after a heavy meal.