Cut up four flounders, or half a dozen perch, onions, and parsley. Put them into three quarts of water, and boil them till the fish go entirely to pieces, and dissolve in the water. Then strain the liquor through a sieve, and put it into a kettle or stew-pan. Have ready a few more fish with the heads, tails, and fins removed, and the brown skin taken off. Cut little notches in them, and lay them for a short time in very cold water. Then put them into the stew-pan with the liquor or soup-stock of the first fish. Season with pepper, salt, and mace, and add white wine or vinegar. Boil it gently for a quarter of an hour, and skim it well.
Provide some parsley roots, cut into slices and boiled till very tender; and also a quantity of parsley leaves boiled nice and green. After the fish-pan has boiled moderately fifteen minutes, take it off the fire, and put in the parsley roots; also a little mushroom catchup.
Take out the fish and lay them in a broad deep dish, or in a tureen, and then pour on the soup very gently for fear of breaking them. Strew the green parsley leaves over the top. Have ready plates of bread and butter, which it is customary to eat with water souchy.
You may omit the wine or vinegar, and flavour the soup just before you take it from the fire with essence of anchovy, or with any other of the essences and compound fish-sauces that are in general use.