Preparation:
Prepare the capon and put thin slices of truffle between its flesh and skin.  Cook the capon liver with 20 g of butter in a frying pan.  Then mix the liver in a food processor with the foie gras, the truffle pieces, the Cognac, some Madeira wine, salt and pepper.  Stuff the capon with this stuffing, attach and season it.  Melt 200 g of butter in a large cast iron casserole.  When it gets dark, place the poultry in this hot butter. Turn the capon several times in order for all sides to get brown.  Then put the casserole, with its lid, in an oven at 220°C for 1 hour and 15 minutes.  From time to time sprinkle the capon with its cooking juice.  At the end of the cooking time, add the carrots and the onion thinly sliced to the casserole, along with the small bouquet garni.  Cover and continue cooking in the oven for another 20 minutes.  Place the capon on a serving dish.  Add the garnish and keep warm in front of the oven.  Pour the chicken stock and the rest of the Madeira wine in the casserole.  Cook for 5 minutes with the vegetables and then drain all of it in a strainer.  Incorporate the rest of the butter to the sauce with a whisk.  Taste and amend the seasoning.  Pour in a saucer.