This is a repost from TKL. My Italian friend said it is best to use green lemons if you can find them.

Limoncello
Posted By: pipeyhawk
Date: June 3rd 1997
Board: recipelink.com Cooking Club

*the zest from 20 lemons (yes, 20-use only the yellow part,paring away any white pith)
(make lemonade from the juice, plant the seeds, & compost the rest :0)-by the way, you must scrub commercially-purchased lemons with a brush first, as they have been waxed)
*750 ml bottle of 100+ proof vodka

combine the lemon peel & vodka in a large well-sealing container (we use a gallon french-lid jar). Store in a cool dark place for 6 weeks.

*4 cups sugar
*5 cups water
boil these together until sugar is dissolved and mixture is slightly syrupy.

*750 ml 100+ proof vodka

add sugar syrup and second bottle of vodka to first jar. swish to combine and let stand in cool, dark place for another 6 weeks.

strain through cheesecloth into smaller freezer-safe bottles. keep one bottle in freezer at all times :0); the rest can stand at room temp.

serve straight up from freezer in chilled shooters, over cracked ice, or in a tall glass with plently of ice & bubble water.

enjoy!