Soap is a rather remarkable creation resulting from the mixture of two common materials. Though it seems odd to say, soap is a salt. Salts are the products of acid+base reactions, in this case the fatty acids contained in vegetable oils and the alkaline properties of lye. Sodium Hydroxide (now industrially produced and known as lye) was once collected and made from ashes and rainwater.
Packing citrus fruit with salt is a technique used the world over, but when we talk about preserved lemon we mentally fly to Morocco. This is a terrific way to make use of your leftover winter crop, concentrating the flavor of lemons into a salty, tender, treat.