2 leeks, trimmed and washed 4 pounds fish heads (gills removed), bones and trimmings 2 yellow onions, sliced 3 carrots, sliced 3 celery stalks with leaves, sliced 7 fresh parsley sprigs 4 fresh thyme sprigs 1 bay leaf 5 quarts of water Salt
Slice the white part of the leeks, reserve the green tops. Place white leeks, fish, onions, carrots, and celery in stockpot. Tie reserved green leek tops, parsley, thyme, and bay leaf with kitchen string. Add to the pot along with the water.
Over medium heat, slowly bring the liquid to a simmer, regularly skimming off the froth on the surface. Cover partially and continue to simmer gently for 30-40 minutes, skimming occasionally.
Strain stock into a large bowl. Discard solids. Season to taste with salt and let cool to room temperature. Cover tightly and refrigerate. Stock may be refrigerated for several days or frozen for up to 6 months.
Use fish parts from mild white fish. Avoid oily, strong-flavored fish, such as mullet, bluefish, salmon, or mackerel.
You may want to try replacing half the water with dry white wine.