Wash and dry the lemons. Use a vegetable peeler to remove the yellow peel, avoiding the white pith. Place the peels in a large jar with a tight-fitting lid.

Pour the vodka over the lemon peels, seal the jar, and store it in a cool, dark place for 3 weeks. Shake the jar every few days to help the infusion along.

When ready to finish, combine sugar and water in a saucepan over medium heat. Stir until the sugar dissolves completely. Let the syrup cool.

Strain the lemon peels from the vodka and discard them. Combine the infused vodka with the cooled syrup. Stir to combine.

Pour the limoncello into clean bottles and seal. Chill in the refrigerator or freezer for at least 4 hours before serving.