It is most commonly used in brandade, a French gratin of mashed potatoes mixed with salt cod, garlic, and olive oil (which is smeared on bread and is heavenly); with ackee fruit in the national dish of Jamaica; in New England fish cakes; in a casserole with potatoes & onions; or battered & fried (as I did).
So, why use dried and salted fish when you could use fresh fillets? NPR compares salt cod to prosciutto, asking "Why eat prosciutto [...] when you could have fresh ham?"
This is not a gratuitous comparison. As Harold McGee writes in his encyclopedic work of food science, On Food and Cooking:
The best of these [salted fish] are the piscatory equivalent of salt-cured hams.
In both, salt buys time for transformation: it preserves them long and gently enough for enzymes of both fish and harmless salt-tolerant bacteria to break down flavorless proteins and fats into savory fragments, which then react further to create flavors of great complexity.I made these fritters in a Girls' Night Out cooking class that I taught on Friday. Having never seen, used, or eaten salt cod before, most of the women in class were skeptical. However, this recipe was a hit!