Remove the bacon rind and cut the bacon into lardons (rectangles ¼ inch across and 1 inch long). Simmer for 10 minutes in 2 quarters of water. Rinse in cold water. Dry.
Saute the bacon slowly in hot butter until it is very lightly browned. Remove to a side dish.
Dry the chicken thoroughly. Brown it in the hot fat in the casserole.
Season the chicken. Return the bacon to the casserole with the chicken. Cover and cook slowly for 10 minutes, turning the chicken once.
Uncover, and pour in the cognac. Averting your face, ignite the cognac with a lighted match. Shake the casserole back and forth for several seconds until the flames subside.
Pour the wine into the casserole. Add just enough stock or bouillon to cover the chicken. Stir in the tomato paste, garlic, and herbs. Bring to the simmer. Cover and simmer slowly for 25 to 30 minutes, or until the chicken is tender and its juices run a clear yellow when the meat is pricked with a fork. Remove the chicken to a side dish.
While the chicken is cooking, boil the pearl onions until tender and saute the mushrooms.
Simmer the chicken cooking liquid in the casserole for a minute or two, skimming off fat. Then raise heat and boil rapidly, reducing the liquid to about 2¼ cups. Correct seasoning. Remove from heat, and discard bay leaf.
Blend the butter and flour together into a smooth paste (beurre manie). Beat the paste into the hot liquid with a wire whip. Bring to the simmer, stirring, and simmer for a minute or two. The sauce should be thick enough to coat a spoon lightly.
Arrange the chicken in the casserole, place the mushrooms and onions around it, and baste with the sauce. If the dish is not to be served immediately, film the top of the sauce with stock or dot with small pieces of butter. Set aside uncovered. It can now wait indefinitely.
Shortly before serving, bring to the simmer, basting the chicken with the sauce. Cover and simmer slowly for 4 to 5 minutes, until the chicken is hot through.
Serve from the casserole, or arrange on a hot platter. Decorate with sprigs of parsley.