Preheat the oven to 325�F. Place the onions in a small saucepan with the bacon strips, cover with cold water and bring to a boil. Drain and rinse with cold water. Melt 1/4 cup of the butter in a 2-1/2-quart, deep flameproof casserole or Dutch oven on the stove. Add the chicken pieces, in batches, skin-side-down, and fry for 10 minutes, or until well browned. Remove from the pan and pat dry with paper towels.
Spoon off the excess fat from the casserole, leaving about 2 tablespoons, then add the bacon, onions and mushrooms. Fry for 3 minutes, or until lightly browned, then remove. Melt the remaining butter in the casserole, add the flour and stir with a wooden spoon, scraping the bottom to prevent sticking. Cook for 3 minutes, or until lightly golden. Gradually add the chicken stock and stir constantly until smooth and heated through. Do not allow to boil.
Return the chicken to the casserole with the bouquet garni, season with salt and pepper and place the bacon, onions and mushrooms on top. Bring just to a boil, cover and bake for 45 minutes, or until the chicken is tender and when pierced the juices are clear, not pink.
Transfer the chicken to a serving dish, then with a slotted spoon, lift out the bacon and vegetables and sprinkle over the chicken. Cover to keep warm and, if necessary, reduce the sauce to a syrupy consistency. Season the sauce to taste with salt and freshly ground black and pour over the chicken. Sprinkle with the parsley and serve with rice, pasta, dumplings or boiled potatoes.