1/2 cup kosher salt, more as needed
additional fresh squeezed lemon juice, as needed
sterilized quart canning jar
Put a couple of tablespoons of salt in the bottom of the jar. Cut off 1/4 inch from the tip of each lemon. You can either quarter the lemons lengthwise or cut them into quarters without cutting through the end – leaving the four quarters intact at the base. Gently open the lemons like a flower and sprinkle a generous amount of salt on the inside of each lemon and then sprinkle more on the outsides. Pack the lemons into the jar, pressing down so that the juice spills out and fills the jar. Keep adding lemons until the jar is full. The lemons should be covered with juice, but if they aren’t, you can add some of that extra lemon juice to top it off. Sprinkle a final couple of tablespoons of salt over the lemons before sealing the jar shut. Let it sit at room temperature for three days, periodically (like once or twice a day) flipping the jar upside down. Move the jar to the refrigerator for three weeks, still flipping the jar upside down ever couple of days. It will be ready when the rinds are soft. When you are ready to use a lemon, rinse off the salt with water and pick out any seeds. Store for up to 6 months.
source: Use Real Butter