1-1/2 cups all-purpose flour
1 cup canola or vegetable oil
1 medium onion, chopped
1 medium green bell pepper, chopped
1 celery rib, chopped
1 cup white button mushrooms, wiped clean and sliced
6 cups chicken broth
5 pounds bone-in chicken thighs
1 bay leaf
Creole seasoning, to taste
Hot rice, for serving
Heat oil in a 4- to 5-quart heavy pot over moderately high heat until hot but not smoking. Stir in flour with a flat metal or wooden spatula and cook, scraping back and forth constantly (not stirring), until roux is the color of milk chocolate, 10 to 20 minutes.
Add onion, bell pepper, and celery. Cook, scraping back and forth occasionally, until onion is softened, about 8 minutes. Add mushrooms and stir to combine.
Add chicken broth and bring to a boil, stirring occasionally until roux is incorporated. Add chicken and bay leaf. Reduce heat and simmer, partially covered, until chicken is cooked through and gravy is thickened, about 1 hour. Remove bay leaf and discard. Stir in Creole seasoning. Serve hot over rice.