Juice the lemons until you have one cup of fresh lemon juice. Strain out any seeds.

In a medium saucepan, combine the lemon juice and sugar over medium heat. Stir until the sugar dissolves completely, then remove from heat.

Once cooled, gently mix in the sparkling water and lemon zest if using.

Pour the mixture into a shallow dish or baking tin and place in the freezer.

After about an hour, when the edges start freezing, use a fork to scrape the ice and fluff it up. Return to the freezer.

Repeat the scraping process every 30 minutes until fully frozen and fluffy, which should take around 2-3 hours.

Once the desired icy texture is achieved, serve in chilled bowls, garnished with fresh mint leaves if desired.