Salt Cod was once an important staple in southwestern Europe, particularly Spain, Portugal and Italy. Basque fishermen, who chased whales all the way to Iceland in Medieval times, discovered the North Atlantic cod fishery. They certainly "discovered" North America long before Columbus, but nobody knows exactly when. Basque fishermen were not literary people, and very secretive about their fishing grounds, and nobody can understand Basque (Euskera) anyway, not even most Basques today.
When Jacques Cartier "discovered" the St Lawrence River in 1535, he reported there were 1000 Basque fishing boats already there. The Basques invented the technique of salting cod, as it is done to this day, and soaking it to make it palatable. They called it "bacalao". The Norwegian Vikings had been freeze drying their cod, but that just wasn't practical for people from more temperate climes.
The photo specimen was 19-1/2 inches long, 7 inches wide and 1-1/2 thick at its thickest point, weighing 2.3 pounds.More on Seafood Products
Today, salting fish to preserve it is not necessary. It can be frozen for storage and transportation, but the unique flavor and texture of salt cod has made it a prized ingredient, particularly in the cuisines of Spain, Portugal and Italy, as well as Canada and Brazil.
Buying: Salt Cod can be found easily in practically any one of the vast number of Italian grocery markets and delicatessens we have here in North America. Be prepared, however, for the price. The photo specimen, 2.3 pounds, was purchased from an Italian market in Los Angeles for 2013 US $11.99 per pound. For many people this relegates it to the realm of "special occasion" foods.
Supermarkets used to stock Lasco brand salt cod in wooden boxes in the refrigerated displays. Perhaps they still do, but I don't know because I can find no evidence of it on the Internet. I've also bought salt cod at one of the local Korean markets, but they sell it skin-on, fins on and bones-in, making it much more difficult to work with.
Storing: Salt Cod should be tightly bagged and kept refrigerated. That way it can be stored for up to a year. Freezing it doesn't do a lot of good due to all the salt - it's never truly frozen and will eventually become rancid, just like ham and other salt cured meats.
Cooking: First you have to soak it in water long enough to leach out the salt - 2 to 2-1/2 days in the fridge, depending on thickness. Change the water twice a day. I put it in a heat sealed 2-mil polyurethane bag and cut a corner off for each draining and refilling, then re-seal. Once it's soaked, just follow the recipe.