• 2 pounds bones and heads of lean, white-fleshed fish, such as snapper or bass, gills removed
• 1 teapoon kosher salt
• 2 tablespoons vegetable oil
• 1 cup diced yellow onion (about 1/2 large onion)
• 1 cup diced fennel bulb (about 1/2 large bulb)
• 1 medium leek, minced
• 2/3 cup diced celery (about 2 large ribs)
• 2 medium cloves garlic, crushed
• 1 cup dry white wine
• 4 cups water
• 2 sprigs flat-leaf parsley
• 2 sprigs tarragon
• 1 bay leaf
• 5 whole black peppercorns

1. 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.
2. In a large saucepan, heat oil over medium-high heat until shimmering. Add onion, fennel, leek, celery, and garlic, and cook, stirring, until vegetables have softened slightly, about 3 minutes.
3. Stir in fish heads and bones.
4. Add wine and cook, stirring, until it begins to steam.
5. Add 4 cups water (liquid should just barely cover heads and bones; if not, add just enough more to barely cover). Add parsley, tarragon, bay leaf, and peppercorns.
6. Bring liquid to a bare simmer, then lower heat so that it stays just below a simmer, with only the occasional bubble.
7. Cook for 20 minutes. Using a spoon, skim off any scum that accumulates on the surface.
8. Strain fish stock through a fine-mesh strainer, then chill.

Fish stock can be kept refrigerated, covered, for up to 5 days or frozen for up to 3 months.