Wash the lemons thoroughly before soaking them in cold water for a day, changing the water two or three times.
Make two fairly deep incisions in the form of a cross in each lemon, starting at the tip. Open the cut as much as possible and fill with salt.
Arrange the filled lemons immediately in one or more preserving jars, packing them tightly and firming them down – it should be difficult to close the lid.
Leave to macerate for 3 weeks.