Rich Fish Stock (Fumet de Poisson)

Combine fish bones and onion in large noncorrosive cattle or Dutch oven. Cook, covered, over low heat, stirring occasionally, until juices are released, about 10 minutes.

Add wine, parsley, thyme, bay leaf, and add enough cold water to cover bones by 2 inches. Heat over medium heat to boiling; boil, uncovered, stirring and skimming surface occasionally, until stock is richly flavored, 15 to 30 minutes.

Strain stock through sieve lined with double thickness of dampened cheesecloth into medium saucepan. Heat over medium heat to boiling; boil, skimming occasionally, until reduced to 1 quart, about 20 minutes. Refrigerate up to 3 days or freeze up to 3 weeks. Heat to boiling before using.