Sterilize the jar and lid by boiling, covered, in water for 10 minutes. make sure not to boil any rubber or plastic in the lids.
Wash the lemons in a vinegar/water solution to make sure all traces of pesticide are washed off before using.
Slice the lemons in quarters, about ¾ of the way down, so they are still connected at the bottom.
Sprinkle 1 teaspoon of sea salt in the lemon, covering the lemon flesh. Pour a layer of salt in the bottom of the jar. Place lemon in the jar, open side down and press down firmly to squeeze out the juice.
Add 2 teaspoon of salt on top of the lemon. Repeat with remaining lemons.
If the juice doesn't cover the lemons when you are done, squeeze some more fresh lemon juice until the jar is full. Place a lid on the jar and store at room temperature for 30 days. Once opened, store in the fridge for up to 1 year.
Recipe can be doubled, quadrupled, etc. Use as many jars as you would like. The lemons will last for up to a year (probably more) in the fridge after they are opened.
Leaving the lemons attached at the bottom gives you a spot to pack them with salt.
If there is not enough lemon juice to fully cover the lemons, add additional juice until the top of the lemons are fully submerged in juice.
To spice up your lemons with some other flavors, try adding bay leaves, peppercorns, cloves, cinnamon, coriander, thyme, ginger, the possibilities are endless. I recommend using about 3 teaspoons of whatever spice(s) you choose to use and mixing it with the salt to evenly distribute it.
Rinse the lemons before using them in recipes. They will likely be slightly slimy before rinsing, which is fine.