Use fish framesthe fish head and bones that remain once a fish has been filletedfrom lean, white-fleshed fish such as red snapper, flounder, halibut, tilefish and porgy. Red snapper yields a particularly tasty stock. The vegetables in fish stock are thinly sliced to cook more quickly.
2 medium leeks, white and tender green only, thinly sliced
1 shallot, thinly sliced
1 small celery rib, thinly sliced
3 fresh thyme sprigs
2 fresh parsley sprigs
1/2 cup dry white wine
1 bay leaf
1 medium tomato, chopped
Rinse the fish frames thoroughly under cold water. In a large nonreactive saucepan or small stockpot, warm the olive oil over moderate heat. Add the leeks, shallot, celery, thyme, parsley and fish frames, bending them to fit into the pan if necessary. Cook, stirring occasionally, until the fish frames turn white and the vegetables are fragrant, about 4 minutes.
Add the wine and cook for 1 minute. Ad 2 1/2 quarts of water, the bay leaf, the tomato and a large pinch of salt. increase the heat to moderately high and bring to a gentle simmer. Skim and reduce the heat to low. Simmer the stock for 20 minutes, skimming often. Slowly pour the stock through a fine strainer into a large heatproof bowl, leaving behind any particles at the bottom of the pan. Season lightly with salt and let cool before refrigerating.