To cook fish properly is very important, as no food, perhaps, is so insipid as fish if carelessly cooked. It must be well done and properly salted. A good rule to cook fish by is the following: Allow ten minutes to the first pound and five minutes for each additional pound; for example: boil a fish weighing five pounds thirty minutes. By pulling out a fin you may ascertain whether your fish is done; if it comes out easily and the meat is an opaque white, your fish has boiled long enough. Always set your fish on to boil in hot water, hot from the teakettle, adding salt and a dash of vinegar to keep the meat firm; an onion, a head of celery and parsley roots are always an acceptable flavor to any kind of boiled fish, no matter what kind of sauce you intend to serve with the fish. If you wish to serve the fish whole, tie it in a napkin and lay it on an old plate at the bottom of the kettle; if you have a regular "fish kettle" this is not necessary. In boiling fish avoid using too much water.
To thicken sauces, where flour is used, take a level teaspoon of flour to a cup of sauce, or the yolk of an egg to a cup of sauce.