Soak the tongues in the refrigerator for 24 hours. Then pour cold water on them and let them bubble. Drain.
Cut all the vegetables into small cubes, put them in a saucepan with the oil and sauté. Add the tongues and cover with water. Cook for an hour and a half. Take out, drain, remove the hard and gristly parts and cover with the liquid strained through a sieve.
Note: Proceed in the same way with veal tongue, but here the cooking time is three hours.