I made a batch of Limoncello last year and I was surprised at how good it came out.  Cut to one year later and I've forgotten how I did it!  I remember the basics, but the key is the addition of a simple syrup after this first step. 

Step 1:
7 organic lemons
1 litre of 100 Proof Vodka.

Using a rasp, take off the zest of the 7 lemons.  The naked lemons left are great for juicing and freezing for later use.   Freeze in small bags (or an ice cube tray ideally) , because I learned from experience that a giant blob of frozen lemon juice is a bit challenging to use.  The zest went into cheap friendly 1.5 litre Carlo Rossi bottle, along with the vodka.  The end product will go into fancy bottles that I buy at Pier 1.

This needs to be covered and let sit for a few weeks.  It's amazing to see the change in the look and aroma of the vodka after a couple of weeks.  Yum!  Place the bottle in a dark place for the next 3 weeks.  Feel free to swirl it around a bit every now and then, and observe the changes taking place.  Part II to follow in a few weeks.