Place lemons in a saucepan, cover with boiling water, place a weight on top to submerge the lemons and leave overnight. Next day, drain lemons and cover with cold water. Set aside for 2 days, changing the water 4 times a day.
Cut lemons into very thin slices, discarding the ends. Sprinkle with salt and refrigerate, covered, for a day, turning once. Next day, place lemons and the salty l