The negrilla wild mushroom (grey knight mushroom, Tricholoma terreum), also known fredeluc or negre (negrito in the Garrotxa region), is particularly good for soups, stews and roast meats. It can be recognised by its grey-coloured cap, which is bell-shaped when young, becoming flatter as it ages. It has a series of broad white gills on the underside which become grey as the mushroom grows in size. The stalk has a firm texture and is fibrous and cylindrical, white in colour, and usually grows to 6-8 centimetres in height. This conserve can be kept for a considerable time, up to two years if it is well prepared.
Clean the mushrooms by cutting off the end of the stalk, and wipe with a damp cloth to remove any impurities. Heat a pan of water, and when it boils, blanch for half a minute. Remove immediately. Place in a wide-necked glass jar. Cover with the same water used for blanching the mushrooms, to which a little salt has been added. Cover the jars and place in a pan covered with cold water. Bring to the boil and simmer for 25 minutes, then remove from heat. Once cold, wipe the jars dry, label them with the name and the date of preparation and store.