Carefully zest the lemons using a vegetable peeler or microplane, being sure to remove only the bright yellow part of the peel and avoiding the bitter white pith. The pith will make your limoncello cloudy and bitter.

Place the lemon zest into your large glass jar. Pour the 750ml of grain alcohol over the zest. Ensure all the zest is submerged. Seal the jar tightly with its airtight lid.

Store the jar in a cool, dark place for a minimum of 4 weeks, and preferably 6 weeks. Gently shake the jar once every few days to agitate the mixture and help infuse the lemon flavor into the alcohol.

After the steeping period is complete, prepare the simple syrup. In a large saucepan, combine the granulated sugar and filtered water. Heat over medium-high heat, stirring constantly, until the sugar is completely dissolved. Do not let it boil vigorously for too long; just enough to dissolve the sugar.

Remove the simple syrup from the heat and let it cool completely to room temperature. This is crucial; adding hot syrup to the alcohol will affect the final product's clarity and flavor.

Once the simple syrup is completely cool, strain the alcohol mixture. Line a fine-mesh sieve with several layers of cheesecloth and place it over a large measuring cup or bowl. Pour the alcohol and zest mixture through the cheesecloth-lined sieve, collecting the infused alcohol. Discard the spent lemon zest.

Pour the cooled simple syrup into the strained lemon-infused alcohol. Stir well to combine thoroughly. The mixture will turn a beautiful opaque yellow color.

Using a funnel, carefully transfer the limoncello into clean, sterilized bottles. Seal the bottles tightly.

Store the bottled limoncello in the freezer for at least 24 hours before serving. Limoncello is traditionally served ice cold as a digestivo. Enjoy!