In a small saucepan over medium heat, combine sugar and water; bring to a simmer. Simmer 1 to 2 minutes or just until sugar dissolves and turns clear. Remove from heat and let mixture cool to room temperature. Stir in the limoncello and lemon juice.
Pour limoncello mixture into a 9-inch square baking dish. Cover tightly with plastic wrap and freeze approximately 45 minutes or until icy at edge of pan.
After 45 minutes, whisk to distribute frozen portions evenly. Cover and freeze again until icy at edge of pan and overall texture is slushy (be sure to scrape the ice crystals off the sides and into the middle of the pan) about 45 minutes.
After 45 minutes, again whisk to distribute frozen portions evenly. Cover and return to freezer and freeze about 3 hours or overnight until frozen solid.
When ready to serve the granita, remove from freezer. Using a fork, scrape granita down length of pan, forming icy flakes. Return to freezer for at least 1 hour. Can be made 1 day ahead. When served, the granita should look like a fluffy pile of dry red crystals.
In a medium bowl, whip whipping cream and vanilla extract until soft peaks form. Cover and store in refrigerator until ready to serve.
To serve, scoop flaked granita into tall goblets or parfait glasses, filling halfway.
Top with whipped cream and sprinkle with lemon zest curls for garnish. Serve immediately with iced tea spoons. NOTE: The Limoncello Granita may be served with or without whipped cream. Both ways are excellent!
Makes 6 servings.