Zest the lemons and add the zest to a clean sterilized jar - Note 1 & 2.
Close tightly and keep in dark area for about 4 weeks. Flip the jar every other day.
NOTES
Note that the white pith is quite bitter and generally of no interest. The best way to get only the peel and not the white pith is to use a Microplane zester. It cuts extra thin taking in only the peel. Just make sure you swipe only once in the same spot on the lemon, else you will get the white pith. If you don't have a zester, peel the lemons using a sharp knife. Then place the cut peel white side up and slowly remove the white pith by slicing with your knife away from you. Keep your fingers behind the knife. Continue until there are no white parts visible on the peel. At this point, you can julienne the peels.
To sterilize the jar place it in the hot oven at 110ºC/230ºF for at least 10 minutes.