Melt the lard in a casserole and add the finely-chopped onion, celery and carrot.

When all the vegetables are lightly coloured, add the ham cut into strips, with the fat discarded. Stir and season with salt and pepper.

Now add the boletus edulis mushroom (carefully wiped clean of all dirt with a damp cloth and sliced paper thin) and the stock. Simmer gently for 15-20 minutes, stirring frequently with a wooden spoon to blend all the ingredients really throughly.

Skim off the fat and sieve the sauce. Return to very low heat and, if necessary, add a knob of butter to bind the sauce together.