5 lb. fish bones
2 Tbs olive oil
4 stalks celery
2 leek
2 cup white wine
Water to cover
2 Onions
8 sprigs of parsley
8 Peppercorns 3 Bay leaf
Place fish bones and heads in a large bowl and cover with cold water. Stir in kosher salt until dissolved. Let stand 1 hour. Drain, then rinse fish under cold running water, washing away any large areas of blood (such as near spine).
In a large saucepan, heat oil over medium-high heat until shimmering. Add onion, leek, celery, and garlic, and cook, stirring, until vegetables have softened slightly, about 3 minutes. Stir in fish heads and bones. Add wine and cook, stirring, until it begins to steam. Add 4 cups water (liquid should just barely cover heads and bones; if not, add just enough more to barely cover). Add parsley, bay leaf, and peppercorns.
Bring liquid to a bare simmer, then lower heat so that it stays just below a simmer, with only the occasional bubble. Cook for 20 minutes. Using a spoon, skim off any scum that accumulates on the surface.
Strain fish stock through a fine-mesh strainer. If excessive liquid, simmer down to approximately 8 cups then chill. Fish stock can be kept refrigerated, covered, for up to 5 days or frozen for up to 3 months.
Re: the fish bones — Heads, spines, ribs, and tails of mild, non-oily, white-fleshed fish. Snapper and bass are two of the most common options, but you could use bones and heads from any appropriate fish, including tilefish, halibut, and cod. Darker-fleshed and oily fish, like salmon, tuna, and mackerel, are not usually used in a classic fumet, since they impart a strong fish flavor.
Clean the bones and heads of anything that might contribute off flavor and color. This means that the gills, which are dark and bitter, have to go, and as much blood as possible should be washed off. There are trace amounts of blood all over fish bones, but you'll find most of it in a vein that runs along the spine, often hidden under a membrane. Removing that blood typically involves a process of soaking and scrubbing. No need for compulsive cleaning here, just do the best you can.
