Ingredients

• 1 tablespoon unsalted butter, softened
• 3 lb mixed bones and heads of white-fleshed fish (such as monkfish, turbot, red snapper, striped bass, porgy, grouper, and/or cod), gills removed and bones and heads rinsed well
• 2 large onions, sliced
• 1 bunch parsley stems (reserve leaves for another use)
• 6 tablespoons fresh lemon juice
• 1 1/2 teaspoons salt
• 10 cups cold water
• 1 1/2 cups dry white wine

Instructions

1. Spread butter in bottom of a 6- to 8-quart heavy pot. Add fish bones and heads, onions, parsley stems, lemon juice, and salt and cook, covered, over moderately high heat, without stirring, 5 minutes. (Mixture will steam in its own juices.) Add water and wine and bring to a boil, then reduce heat and simmer, uncovered, skimming any foam, 25 minutes.
2. Pour stock through a fine sieve into a large heatproof bowl, pressing on and discarding solids. If not using stock immediately, cool, uncovered, before chilling, covered.