Cook the pig’s head and tongues for 3 hours in a large volume of water, along with the bouquet garni, the leeks and the onions: the meat must be very tender. Peel the tongues and allow the whole mixture to cool.
Make a vinaigrette by mixing the mustard, vinegar and the oils; slice the head and tongues as thinly as possible;
chop the bulb spring onions.