For limoncello, wash the lemons carefully in warm water, rubbing with a fine brush if necessary. Peel the lemons with a peeler, remove the bitter white lemon skin. Cut the peels into strips.
Place the peels in a glass jar or earthenware pot and pour the alcohol over them. Cover and let steep in a cool dark place for 20 days. During this time, shake daily.
Heat the sugar with a liter of water in a pot until it dissolves. Let the sugar water cool and mix it with the limoncello mixture. Now let it mature in a cool, dark place for another 20 days.
Hang a large sieve in a pot and line it with a straining cloth (muslin cloth). Filter the limoncello mixture.
Bottle the limoncello, seal it immediately and let it rest for another 3 months before tasting it for the first time.