An essential in the fridge for seasoning all kind of foods from salads to stews to pasta, curries. A salt lemon is just a great addition for some sour, salty extra taste.
And they are so easy to do! I use often mostly squeezed (organic) lemons and then put them into a lot of salt. More salt than I would use for a “regular” salt brine. Also, I would add squeeze one lemon to have more liquid and maybe add a little bit of filtered water just to make sure the lemons are in the salty liquid. After 1-2 weeks outside the fridge, they move inside the fridge and are kind of immortal.
(On the foto, the salt settled down after a bit on the bottom of the jar. But those are already fermented and from my fridge. So for the fermentation process it would be important that they are less “dry” on top to prevent mold.)
