Recipe: Truffle Capon with Chestnuts

The day before:
Completely debone the capon, lightly salt and pepper the meat, grate a little truffle.
Form into a roast by wrapping the meat in the skin.
Place the meat pieces head to tail, the thin parts resting on the thick parts, so that the roast has a regular and cylindrical shape at the end.
(Make sure to remove the tendons from the legs and fillets).
Tie quite tightly.
Lard the poultry with truffle slices, by making incisions in the skin between the string turns. Lightly salt the skin.
Reserve in the cold, tightly wrapped in plastic wrap.
Prepare a poultry stock. (Capon carcass and various trimmings, studded onion, leek, carrot, celery, bouquet garni, pepper in mignonnette, salt, straining, reduction).
The same day:
Heat the oven to 180°.
Place the capon in a cocotte in two tablespoons of olive oil, and sear it over high heat, turning it to color it on all sides. Salt and pepper.
Put the cocotte in the oven, uncovered, adding an onion cut into quarters, a few sprigs of thyme and a glass of water.
Cook for 60 minutes, turning the piece regularly.
Braise separately in a cocotte, in a knob of clarified butter, the mushrooms and onions, salt and pepper.
Braise the chestnuts in the same way for 5 minutes, salt, pepper, then moisten with a small ladle of poultry stock (defatted), and keep for another 15 minutes over low heat.
At the end of cooking, remove the capon from the cocotte and let it rest covered.
Degrease the cocotte, keeping only the lean cooking juices.
Deglaze with a splash of balsamic vinegar, scraping up the juices well, then moisten with the poultry stock.
Bring to a boil and pass through a fine sieve.
Return to the heat, add the juice released by the resting piece.
Whisk four tablespoons of crème fraîche, and incorporate the sauce. Mont