1. Wash lemons, in hot water and dry. Using a vegetable peeler, remove the zest from each lemon in wide strips, leaving behind as much of the white pith as you can. (Reserve whole lemons or freeze their juice in ice cube trays for another use.)

2. Put zest and grain alcohol into a large glass jar with a tight-fitting lid, pressing down on zest to submerge, if necessary. Cover tightly and set aside in a cool, dark place to let infuse for 48 hours.

3. Cook sugar in 4 cups of water in a large pot over medium-high heat, stirring occasionally, until it comes to a boil. Remove syrup from heat and let cool completely.

4. Strain zest from alcohol through a sieve set over the pot of syrup; discard zest. Stir to combine and return to the jar. Limoncello is ready to serve at this point. Store, tightly sealed, at room temperature for up to 3 months.