Wash the tongue thoroughly and put into a saucepan.
Cover with cold water, bring to the boil and drain.
Curl the tongue and put into the Slo cooker.
Add sufficient boiling water to cover.
Add the onion, celery, carrot, peppercorns, bay leaves, bouquet garni and salt.
Cook for the recommended time.
Remove tongue and reserve stock
Plunge the tongue into cold water and remove the skin and gristle at once.
Put into a small cake tin or souffle dish.
Dissolve the gelatin in 300ml (1/2 pt) of the strained stock.
Pour over the tongue.
Cover with a small plate or saucer and press with a heavy weight.
Chill until set.