Using a vegetable peeler or zester, gently peel off the skin of the lemons, avoiding the white pith.

Add the lemon peels into a large glass container, pour in the vodka, and seal it tightly. Allow to infuse in a cool, dark spot for at least two weeks, ideally one month.

In a medium pot over medium heat, combine sugar and water, stirring until the sugar dissolves. Remove from heat and chill in the refrigerator for at least 10-15 minutes.

Strain the limoncello concentrate using a fine-mesh strainer and press down on the lemon skins to extract as much liquid as possible. Discard the solids.

Mix the cooled simple syrup with the strained limoncello concentrate. Adjust sweetness to preference.

Transfer the limoncello into glass bottles and label them if desired.

To serve, fill a glass with ice, pour in your homemade limoncello, and top with sparkling water.