Make sure you use fresh lemons that are not waxed, try to find organic lemons or get them right from an orchard.
12 lemons
2 liters vodka
6 c sugar
3 c water
Remove the zest from the lemons with a potato peeler, make sure you don’t get any of the white pith. In a clean glass container mix the vodka and zest. Cover and place in a cool, dark spot for 4 weeks. Mark on a calender so you don’t forget 
Strain the vodka mixture into a pitcher to remove the zest. Pour the mixture into a bottle or evenly into multiple bottles. Make a simple syrup: in a saucepan mix the water and sugar. Bring to a boil over high heat, stirring constantly. Reduce the heat to medium and simmer until all the sugar is dissolved. Remove from the heat and cool.
Pour the simple syrup into the vodka mixture, divide it evenly. Store in the freezer for up to one year and serve right from the freezer in small, chilled glasses.
See earlier post for Limoncello-Floats
[...] See a later post for an excellent Limoncello Recipe. [...]