Wash lemons with a vegetable brush and hot water to remove any residue of pesticides or wax, then pat dry.

Carefully zest the lemons, avoiding the white pith.

In a large glass jar, combine one bottle of vodka with the lemon zest.

Cover the jar and let it sit at room temperature in a cool dark place for 10 to 40 days.

Combine sugar and water in a saucepan and cook until thickened into a syrup (5-7 minutes).

Let the syrup cool completely.

Add the cooled syrup and the second bottle of vodka to the lemon zest mixture.

Allow the jar to rest for another 10 to 40 days.

Strain the liquor through a fine-mesh sieve or cheesecloth, discarding the lemon zest.

Bottle the limoncello and store in the freezer. Serve ice cold.