Wash and scrub the lemons and trim off the ends.
With a sharp knife, cut the lemon in half lengthwise, from the top of the lemon down to about 1/4" from the base. Do not cut all the way through. Turn the lemon 180° and cut again, effectively quartering it, but don't cut all the way through. Repeat with the other 4 lemons.
Sprinkle salt inside the cut pieces of the lemons and then place the lemons in the clean jar. You may have to squeeze them to get them in, this is ok.
Add the rest of the salt to the jar and then add the lemon juice until you cover the lemons in the juice. Place a lid on the jar and turn it upside down a couple of times to make sure the salt starts to dissolve.
Leave the lemons on the counter for a couple of days, turning the jar every 12 hours or so to make sure the salt and juice are being combined. On day 3, place the jar in the refrigerator. According to Wolfert's book they need to cure for 30 days, but I think they may be ready as soon as 3 weeks. Every so often, turn the jar upsidedown in the refrigerator. When the lemon peels are soft, they are ready. Preserved lemons can be kept in the refrigerator for up to 6 months (or according to some, much longer).