Wash the lemons thoroughly to remove any wax or pesticides.
Use a vegetable peeler to zest the lemons, avoiding the white pith.
Place the lemon zest in a large glass jar.
Pour in the vodka over the zest and seal the jar tightly.
Store in a cool, dark place for at least 7 days, shaking occasionally.
Prepare a simple syrup by boiling water and sugar until dissolved.
Allow the syrup to cool before adding it to the lemon-vodka mixture.
Strain the mixture through a fine mesh sieve to remove the zest.
Pour the limoncello into clean bottles and seal them.
Refrigerate or freeze before serving for the best flavor.