Step 1: Wash and scrub the lemons or limes; there's often a thin layer of wax or other preservative on the peel. Cut each fruit nearly into four pieces by making two cuts at right angles to each other from one end of the fruit almost to the other, leaving enough uncut that fruit can be opened without falling apart, about 1/2 inch.
Step 2: Generously salt the exposed flesh, using at least three tablespoons per pound of lemons.
Step 3: Put the salted fruits in a big, clean jar and cover with fresh lemon juice or water. Lemon juice gives a better flavor, but resist the temptation to use bottled lemon juice, which gives an unpleasant metallic quality. Put on the lid and leave the jar at room temperature for four or five weeks.