The granita is a cross between sorbet and Italian ice, and there’s a cool trick to get the right icy texture. My version is made with watermelon and a little vodka for a perfect adults-only frozen treat.
Slice, peel, and cube 6 cups of watermelon. Combine coarsely chopped watermelon, sugar, and lime juice in a bowl and let stand until macerated and juicy, 25 minutes.
Process in a blender until just smooth, then pass through a China cap using the back of a ladle. Transfer to a shallow metal tray and remove the foam on top. Freeze, stirring and scraping occasionally with a fork until crystals form and granita is frozen (2–4 hours). Every 20–30 minutes, scrape a fork through the mixture to create the crystals.
To serve, divide finely diced watermelon among chilled serving glasses and top with granita. Drizzle with vodka (optional) and serve immediately.