Place the tongue, vegetables, herbs and peppercorns in a saucepan with enough hot water to cover.
Bring to the boil, cover with the lid and simmer gently for 3 hours until tender.
Remove the tongue, cut away the root and skin.
Cut into slices and place in a casserole.
Make a brown roux by melting the butter until it is foaming and turns golden on a high heat, add the flour and allow to brown.
Add 300 ml (1/2 pint) of cooking liquid and cook until smooth and pale brown.
Sieve if necessary, add the Madeira and cook for about 2 minutes.
Pour over the sliced tongue in the casserole.
Cover and return to the oven for 30 minutes.