This way of preserving very young porcini (Boletus edulis) comes from Fivizzano in the Lunigiana behind La Spezia, a famous fungi region. It can be successfully applied to very young field agarics (gills still pink), to baby chanterelles (Cantharellus cibarius) and to orange milk mushrooms (Lactarius deliciosus, L sanguifluus, etc).
So, using fungi freshly gathered in an immature state, remove the base of the stems, but otherwise leave them whole. Clean them well, put them in an earthenware or enamel pan and just cover, half and half, with white wine vinegar and water, adding
Next day: put them into clean glass jars with
Cover with olive oil and close with an airtight lid.
Leave for at least six weeks to allow the oil time to overcome their impregnation with vinegar. Serve as an hors d’oeuvre.