Scrub 6 of the lemons and dry well. Quarter the 6 lemons, cutting from the top to within ½inch of the bottom, sprinkle salt on the exposed flesh, then reshape the fruit. Toss with the remaining salt and pack the lemons into a 3- or 4-cup dry, sterile Mason jar with a glass or plastic-coated lid.
With a wooden spoon, gently push down on the lemons. Squeeze the juice from the remaining 4 lemons and pour into the jar. Close the jar tightly and let the lemons ripen at room temperature for 30 days, shaking the jar each day to redistribute the salt and juice. (Within a few days the salt will draw out enough juice to completely cover the lemons.)
For longer storage, add olive oil to cover and refrigerate for up to 1 year. Rinse the lemons before using.
Variation: 7-Day Preserved Lemons
Scrub 2 ripe lemons and dry well. Cut each into 8 wedges. Toss them with ⅓ cup coarse sea salt and place in a ½-pint glass jar with a glass or plastic-coated lid. Pour in ½ cup fresh lemon juice. Close the jar tightly and let the lemons ripen at room temperature for 7 days, shaking the jar each day to distribute the salt and juice. To store for up to 1 week, add olive oil to cover and refrigerate.