Roughly chop the fish bones and place them in a large bowl or stockpot. Cover with cold water and soak for 1 or 2 hours to remove any remaining traces of blood.

Discard the green portion of the leeks. Trim and rinse the whites thoroughly, then roughly chop. In a large stockpot over high temperature, heat the butter until bubbling. Add the leeks, onions, celery, garlic, and mushroom stems and saute until they begin to give off their aroma, 3 or 4 minutes. Add the wine and bones, reduce heat, and sweat the mixture, covered, for about 8 minutes. Add the thyme and water and simmer, uncovered, for 25 minutes more. Strain through a fine sieve into a bowl and use immediately, or allow to cool to room temperature before refrigerating.

This stock keeps in the refrigerator for up to one week and can be frozen.

Per serving: 528 Calories (kcal); 14g Total Fat; (30% calories from fat); 8g Protein; 63g Carbohydrate; 31mg Cholesterol; 193mg Sodium Food Exchanges: 1/2 Grain(Starch); 0 Lean Meat; 9 1/2 Vegetable; 0 Fruit; 2 1/2 Fat; 0 Other Carbohydrates