Choose smooth, thin-skinned, unblemished lemons. Scrub them well. Make two vertical cuts in a cross to within about 1/2 inch of their base, so that they still hold together. Put 1/4 teaspoon of salt into the center of each lemon and press them closed. Pack tight in sterilized glass jars. Sprinkle 1 tablespoon of salt and the strained juice of 1 lemon into each jar. Top off each jar with boiling water and seal. Leave them for 3 to 4 weeks. 

To use lemons, rinse well under cold water and discard the flesh and pith, retaining peel only.