Wash the jar and its cover in hot water (or use the dishwasher). Spoon about a teaspoon of the salt into the bottom of the jar. Rinse the outside of the lemons. Cut the tip from the pointy end of each lemon. Cut the lemons into quarters. Add a few quarters to the jar, then sprinkle with salt and press down on the lemons to extract the juice (I use a wooden spoon). Keep repeating this step, layering the lemon quarters and salt and pressing out the juice) until all has been used. Close the jar. Keep the jar at room temperature for one week. Turn the jar upside down occasionally. Transfer to the refrigerator for another 3 weeks (turn the jar occasionally). The peels will become translucent when they are ready for use. Use a tongs or fork to remove pieces of lemon as needed.
Ronnie Fein is a cookbook author, food writer and cooking teacher in Stamford. She is the author of The Modern Kosher Kitchen and Hip Kosher. Visit her food blog, Kitchen Vignettes, at www.ronniefein.com, friend on Facebook at RonnieVailFein, Twitter at @RonnieVFein, Instagram at RonnieVFein.