Remove wide strips of zest from one of the limes, using a vegetable peeler. Combine with the sugar and 3/4 cup water in a small saucepan. Bring to a simmer, stirring to dissolve the sugar. Turn off the heat and let cool to room temperature. Discard the strips of zest.
Finely grate the zest from the remaining 2 limes and set aside. Juice all 3 limes and blend the juice, watermelon, prosecco, Campari and sugar syrup in a blender until smooth, about 1 minute. Pour into a 9-by-13-inch glass baking dish and freeze, 2 hours. Use a fork to scrape the ice crystals toward the center of the pan, then continue freezing, scraping every 45 minutes, until the mixture is no longer slushy, about 4 more hours.
Scoop into paper cones or cups. Drizzle with the peach nectar and sprinkle with the grated lime zest. Garnish with watermelon wedges.
Photograph by Ralph Smith
Courtesy of Food Network Magazine