This recipe is adapted from Joan Nathan's "New American Cooking" and is used to make Quinoa with Asparagus and Preserved Lemon Dressing.
Leaving one end intact, cut lemons lengthwise into quarters. Using your fingers, stuff about 2 tablespoons salt inside each lemon, close them, and transfer to an 8-cup, sterilized, wide-mouth jar.
Measure juice in a liquid measuring cup, add to jar along with half that amount of water, making sure liquid almost covers lemons. Add more freshly squeezed lemon juice, if necessary.
Loosely cover jar and let stand, at room temperature, for 2 days, shaking the bottle each day.
If there is room, add more cut lemons with salt and add to jar, covering with more lemon juice, if necessary, and olive oil. Cover jar and let stand at room temperature at least 3 weeks.
To use lemons, rinse with water. Remove seeds and pith and discard. Use peel as desired.