Wash the lemons well, scrubbing any wax off if you were unable to get unwaxed. Trim the stem end off the three whole lemons.
Add around ½ tbsp salt to the bottom of a sterile mason jar or medium jam jar.
Sit a lemon with the trimmed end down on a cutting board and cut down to leave just a little still joined at the bottom (around ⅓in/1cm from bottom). Cut again at right angles to make a cross shape.
Slightly open up the lemon and sprinkle 1/t tbsp salt inside the cuts.
Place the lemon in the jar then repeat with 2 more lemons.
Press the lemons down in the jar well to release some of the lemon juice. Take another half lemon and squeeze more juice into the jar, then split this lemon half in two and add to the jar, pushing half down each side. Sprinkle the remaining salt over the top and put the lid on the jar.
Leave the jar overnight in a cool, dark place then the next day push down the lemons again to release more juice. If needed, add more lemon juice to ensure the lemons are just covered.
Cover with lid again then leave the jar at least 3 weeks to mature, in either a cool place or fridge. The lemons are good to use when the skin has softened and white pith is slightly opaque. Rinse off the piece you plan to use before using.