Larousse Gastronomique
Mushroom ketchup or catsup. Ketchup aux champignons.
Put in a salting jar layers of fresh sliced mushrooms (about ½ inch in depth) and sprinkle each layer with table salt, pepper and allspice.
Leave the mushrooms in the salt for 5 or 6 days in a cool place.
Press the mushrooms to extract all the juice. Boil this juice. Season with pepper, thyme, bay, ginger, majoram, and a little tomato paste.
Leave it to cool. Filter and bottle.