At the bottom of the page is an excerpt from a web site that had the best recipe which I have slightly modified.
20 large lemons
1.75 L bottle of Everclear (+ 1-750 ml bottle)
1.75 L bottle of vodka
11 cups sugar (4 lb bag + 3cups)
12 cups water
Note: This makes about 11 (750 ml) bottles
Wash and dry the lemons. Using a vegetable or potato peeler, remove the yellow skin, taking care to not include much white pith, as this will make it bitter. The size of the peels doesn't matter. Place the lemon skins in a large jar and add the Everclear and vodka. Cover tightly and place in a cool, dark place. Gently stir or shake every 7 days. After 5 or 6 weeks, remove one of the peels and bend it; if it snaps in two then proceed with the recipe. If it still bends without breaking, continue aging for a week or more until the peel does break in two.
In a large saucepan, combine sugar and water and cook over medium-high heat just until the sugar dissolves. Do not allow mixture to boil. Remove from the heat and allow to cool to room temperature. Use a large enough pan to also hold the alcohol, later.
Gently remove the peels from the alcohol with a strainer or slotted spoon. Discard the peels. Strain the mixture through a few layers of cheesecloth or coffee filter. This could take a fair amount of time and several filters. It depends on how 'clear' your want it to look.
After straining, add the alcohol to the simple syrup and stir to combine. Make sure that the simple syrup is not hot because alcohol evaporates at a low temperature.
Pour into smaller bottles, seal and store in a cool, dark place until ready to serve. Some recipes suggest that you should wait another 6 weeks before serving for the best results.
What do we do with all the peeled lemons? Make lemonade!
6 lemons or 1 cup juice
1 cup sugar
6 cups water
First created on the island of Capri, this smooth, refreshing and deceptively strong liqueur was quickly adopted by Sicily and other citrus-growing regions of Italy a little over a century ago. Limoncello is often served chilled as an after-dinner digestivo, but is quickly becoming popular with bartenders and mixologists around the world as an ingredient in cocktails.
I'll admit, there are many recipes for limoncello that are faster to make, and trust me, I've tried a lot of them. What I've learned from a lot of testing is that time and patience will give you an extremely refinned and smooth liqueur. Infact, I have had a couple bottles tucked away for over a year now that just seem to get better and better.
Since limoncello is made solely from the skin of the lemons, the end result is surprisingly sweet with a strong lemon flavor. Traditionally made with lemons, you'll find almost any citrus fruit will work. My personal favorite is pink grapefruit, but oranges, tangerines and especially blood oranges make exceptional variations. When I tried a lime version I found it a little too bitter on its own but fantastic when added to cocktails, like mojitos or vodka tonics.