As a born-and-bred Boston kid, chowder holds a special place in my heart, and fish-based chowders doubly so, as a fish chowder was the very first dish I ever got to stick on a real restaurant menu. It was early on in my career, when I was working the lunch shift at Barbara Lynch's No. 9 Park in Boston; Jason Bond, the chef de cuisine, tasked me with coming up with a dish that would use up the scraps of cod, striped bass, and salmon that we had kicking around every day after portioning whole fish.
The fish chowder I came up with there started with a fumet made from fish heads and bones and flavored with onions, celery, bacon rinds, and fennel. To that I added little cubes of potato and celery simmered in milk, along with rendered lardons of salt pork and a splash of heavy cream reduced with more aromatics to bind it all together. I added the fish chunks just before serving so that they just barely cooked through. We garnished the whole thing with homemade oyster crackers.
It was creamy, rich, and satisfying, and totally impractical for any kind of home cooking. Restaurants are often in the business of complicating things; making things 90% more difficult in pursuit of 10% better flavor.
At home, I take a much more traditional one-pot approach to chowder-making. While the resulting dish may not quite reach the lofty heights of fine dining, the results are still creamy, satisfying, delicious, a great use of leftovers or inexpensive fish, and—most important—really, really easy.
Having previously explored the history and science of chowder in this article about clam chowder, I'll offer only the briefest recap. Chowders have long been made in New England (the oldest printed recipe dates back to 1751), and what started as a hearty stew of dried fish, dried meat, and hardtack biscuits layered in a pot and simmered in water has evolved into dairy-based soup flavored with salt pork, onions, celery, and potatoes.
To make mine, I start by rendering sliced bacon or salt pork in a large saucepan, letting it cook down until it just starts to brown around the edges. The easiest way to do this is to cover the pork with a little bit of water at the start. The simmering water kickstarts the rendering process so that by the time it evaporates, they are ready to melt off their fat in earnest.
Whether you pick salt pork or bacon depends entirely on your own taste and mood. Either will work.
Once the pork has rendered its fat, I add a chopped onion and some chopped celery, sautéing just until aromatic, then I add a couple tablespoons of flour. Flour is a contentious ingredient in chowders. Some insist that chowders should be flour-free, its only thickening coming from potatoes, reduced dairy, and the oyster crackers you crumble into it. But omitting flour can cause some difficulties with getting a stable emulsion in the broth. You're much more likely to end up with a greasy-looking bowl if you go flour-free.
In my own clam chowder recipe, I omit the flour and combat the problem of greasiness by straining the broth and blending it just before serving the soup. But for this recipe made with fish scraps, that all seems a little tedious, so I compromise by using just a couple tablespoons of flour. It's enough to keep the liquid from fully breaking, but not so much that you end up with a chowder that has the consistency of spackle (as is unfortunately too-often the case, even in New England).
If you have the wherewithal to plan ahead, you can ask your fishmonger for a fish head, and simmer it together with aromatics to make a quick fumet, then you can use that fumet as the base for this soup. For those of us who don't always think far enough in advance to do that, there's bottled clam juice.
Bottled clam juice is one of those ingredients on supermarket shelves that always made me think eeeuugh—until I actually tried it, that is. Unlike most boxed broths and stocks, which often contain very little actual broth (especially beef broths), clam juice is literally just clam juice, water, and salt. Nothing else whatsoever. It's a fantastic flavor booster for any kind of seafood stew or soup (or even a seafood pasta).
I stir in a cup of clam juice and a quart of milk into my chowder along with a bay leaf and a diced potato (russet or Yukon gold both work), bring it to a simmer, and let it cook just until the potatoes are tender and the soup is nice and rich.
Finally, just before serving I toss in the fish, which I've cut into bite-sized pieces that cook through with just a moment or two of simmering.
In New England the only garnish you might see with chowder is oyster crackers, freshly ground black pepper, and maybe a dash or two of hot sauce. In my house, I like to add some chopped fresh herbs to it too (dill is particularly nice with salmon). I hope I don't get my official New Englander membership card taken away for that transgression.