Wash your lemons.
Cut an X into the base of 2 to 3 lemons (or however many will fit in your jar).
Press kosher salt into the cuts in the lemon. Then press them all into the glass jar.
Squeeze the juice from the remaining lemons (strain to remove seeds) and add juice to the jar till the lemons are fully covered.
Store in a cool, dry place for at least one week before using.
After opening, store in the refrigerator for up to 6 months.