Cut up one good-sized, peeled and well-washed carrot, with a sound onion, and half a bunch of parsley roots, also cut up; brown them in a glassful of white or red wine, according to the fish; add to it any well-washed pieces of fish-heads and a pint of water. Season with half a pinch each of salt and pepper. Boil well for five minutes; let cool; strain through a napkin or a sieve into a jar, and use when needed. Always avoid straining anything acid into tin or copper vessels - to prevent blackening.