Step 1: Cut the rinds off of the lemons leaving the white part behind. Put these with the alcohol into a glass container or bottle and allow the alcohol to infuse the lemon rinds for 3-4 days. If you're using yellow (ripe) lemons, you can squeeze about a tablespoon of juice into the alcohol to ensure you get a strong flavor.
Step 2: After 3-4 days, separate the rinds from the alcohol (squeeze the rinds to extract any juice from them) and throw the rinds away. Boil the 1/2 liter of water and then add sugar. Stir until thoroughly dissolved.
Step 3: Allow the sugar/water mixture to cool then add to the lemon-infused alcohol. Mix well then filter into suitable bottles. Step 4: Store limoncello in the freezer so that it forms a thick almost syrup liquid. Pour into chilled shot glasses and drink.