Cook bacon in a deep 12-inch heavy skillet over medium heat, until crisp, then transfer to paper towels to drain; cool and crumble. Reserve bacon fat.
Meanwhile, in a shallow dish, stir together flour, salt and black pepper, set aside.
Heat bacon fat in same skillet over medium-high heat until hot. Dredge half of chicken in seasoned flour, knocking off excess, then brown in fat, turning occasionally; transfer to a platter. Dredge and brown remaining chicken in same manner.
Pour off all but 2 tablespoons fat from skillet, then reduce heat to medium. (Use vegetable oil if you do not have enough fat.) Add remaining 2 tablespoons flour, cook roux, stirring constantly, until lightly browned, about 2 to 3 minutes.
Add onions, cook, stirring occasionally, until browned, 5 to 8 minutes. Add stock, herb sprigs, cayenne and bay leaf, then bring to a boil, stirring up brown bits. Add chicken with juices, then reduce heat and simmer, covered, until chicken is tender, 45 minutes to 1 hour.
Discard bay leaf and herb sprigs. Stir in crumbled bacon and fresh chopped parsley. Serve over hot cooked rice.