Capon with Wild Mushrooms and Mint Béarnaise

If you cannot find a capon, any large chicken, even a roasting chicken, will do for this recipe. The main thing is not to use a little, 1½-pound chicken that will cook so quickly that the broth will get no flavor from the meat and the meat no flavor from the vegetable broth. The same recipe could be used for game birds, and the size and age of any of the birds will determine the cooking time.