Wash the lemons thoroughly under hot water and place them in a large glass. Cover with cold water and put in a cool place for 4 days. Change water daily.
Then drain the lemons and cut off a tip from each lemon. Cut the fruit crosswise all around and squeeze out a little. Collect the juice. Add about 1/4 teaspoon of salt to each cut.
Place the lemons in a sterilized preserving jar. Season with 1 tsp salt and lemon juice. Add boiling water until the lemons are covered with water. Leave to soak for about 3 weeks.