This dish is of very ancient origin, and the recipe I give is the traditional one. In some parts of France, red wine is used instead of white.
Roast the birds and, while they are being roasted, put the chopped shallots, the herbs, etc. in a small saucepan with the white wine, and simmer gently till reduced to about one third. When the birds are nearly done, carve them carefully, removing all the flesh from the carcass. Place the pieces of duck in a saucepan, with the brandy, and set alight. When the brandy is burnt out, add a little Espagnole sauce, cover with a lid and keep warm. Chop up the bones or pound them in a mortar, and add to the wine and shallots, mixing well. Add the remaining Espagnole sauce, stir well, and simmer gently and skim carefully. Cook for about 20 minutes. Five minutes before serving, strain half the sauce over the pieces of duck, and place the saucepan over a slow fire, but on no account should the sauce be allowed to boil. Remove the remainder of the sauce from the fire, add a few small pieces of butter, not quite 1 oz. altogether, and strain over the birds. Garnish with the cooked mushrooms, a few sliced truffles, and croûtons of fried bread.