This takes about a month from start to finish, but it's worth the effort! Maximize your efforts and make a double or triple batch.
1 liter vodka
3 cups white sugar
4 cups water
Zest the lemons, and place zest into a large glass bottle or jar. Pour in vodka. Cover loosely and let infuse for one week at room temperature.
After one week, combine sugar and water in a medium saucepan. Bring to a boil. DO NOT STIR. Boil for 15 minutes. Allow syrup to cool to room temperature.
Stir vodka mixture into syrup. Strain into glass bottles, and seal each bottle with a cork. Let mixture age for 2 weeks at room temperature.
Place bottled liqueur into the freezer. When icy cold, serve in chilled vodka glasses or shot glasses.