Wash the lemons thoroughly under warm water to remove any wax or dirt. Dry them completely with a clean towel.

Using a vegetable peeler, carefully peel the zest from the lemons, avoiding the white pith as much as possible, as it can make the limoncello bitter.

Place the lemon peels in a large glass jar and pour the vodka over them. Seal the jar tightly.

Store the jar in a cool, dark place for at least 7 days, shaking it gently once a day to help infuse the flavors.

After a week, prepare the simple syrup by combining water and sugar in a saucepan. Heat over medium heat until the sugar dissolves completely, then let it cool to room temperature.

Strain the lemon-infused vodka into a large bowl, discarding the lemon peels. Mix in the cooled simple syrup.

Pour the limoncello into clean bottles and seal tightly. Store in the freezer for at least 4 hours before serving.