Combine the sugar and 1 cup water in a saucepan. Bring to a boil and stir until sugar is dissolved. Remove from heat and place in the refrigerator until cold, about 1 hour.
Using the finest grater you have, lightly scrape the skin of 1 lemon, removing only the top surface of the peel. Squeeze out the juice and remove the seeds from both lemons.
Open the Champagne or sparkling wine, and pour it into a 9 by 12 by 2-inch pan. Mix in the simple syrup, lemon juice, and grated zest. Place mixture into the freezer. Check after 30 minutes. Using a wooden spoon, break up any ice formed on the sides and stir into the rest of the liquid. Continue to freeze and repeat this procedure every hour for at least 3 hours. Before serving, fluff the granita by "chopping" up any clumps with the spoon or gently whisking the frozen mixture. Spoon into small glasses or cups and serve.
Recipe courtesy of Bobby Flay