Put 1 cup water and sugar in a medium saucepan and bring to a boil.
Once boiling, lower heat and let mixture simmer for about 10 minutes, until sugar is completely dissolved and syrup has thickened (note that it will continue to thicken as it cools).
Keep syrup in bowl or pour into a mason jar and place in fridge to cool completely before using.
In a large bowl, whisk together cooled simple syrup, freshly squeezed lemon juice, lemon zest (if using), remaining ½ cup water, and a pinch of salt.
Pour into a metal or glass 8x8 or 9x9 dish (metal will help mixture freeze quicker). Place in freezer.
After about 45 minutes, remove from freezer and use a fork to begin scraping at the ice crystals forming around the edges to break into smaller pieces.
Place the dish back in the freezer and 30 minutes later, check again and continue to scrape with a fork. After about 2 hours, you should have it completely scraped and the mixture should be completely uniform and flaky.
Serve in bowls topped with more lemon zest, if desired.