Slice the ends off each lemon and stand them on one end.
Using a small, sharp knife, carefully make 2 vertical cuts three-quarters of the way through each lemon, as if cutting into quarters, but keep the bases intact.
Stuff 1 tablespoon of the salt into each lemon, then pack into a large sterilized jar and seal tightly.
Store in a cool place for 3–4 days to soften the skins.
Press the lemons down into the jar until tightly packed, then cover with the lemon juice.
Seal the jar and store in a cool place for at least 1 month before using.
Use within for 3–4 months.
When ready to use, rinse off the salt and pat dry with kitchen paper.
Cut the lemon into quarters and, using a small, sharp knife, remove the flesh, seeds and pith.
Finely slice or chop the rind and use as required.