Interesting that no one has mentioned salt cod. Around here fish cakes
= salt cod. My fish cakes have only 4 ingredients.

Salt cod
Potatoes -- boiled & mashed without adding anything
Onion (or green onion)
Pepper
Some folk add parsley.

Using salt cod of course requires bringing it back to an acceptable
level of saltiness. Done usually by soaking overnight (if using solid
cod) or by doing a bring to a boil/simmer/drain and repeating until
palatable.

Once cod has cooled, flake it (or put through the food processor). Mix
with potato, onion & pepper. Form into patties & fry in butter. Can
be rolled in flour first but it's not necessary.

That is normally my Ash Wednesday/Good Friday suppers.

Gabby