Season the chicken with salt and pepper, and dust it with flour. Shake off excess flour. Heat the oil in a large, heavy, dry pot over high heat until it reaches its smoking point, about 3 minutes. Sear the chicken in the hot oil until it is golden brown, about 5 minutes on the first side and 4 minutes on the second. Remove the chicken from the pot.

When the oil has returned to the smoking point, make a roux by slowly adding the flour to the oil, stirring constantly over high heat with a wooden spoon until the roux is the color of milk chocolate, about 3 to 5 minutes. Scrape the sides and bottom of the pot as you stir. Be careful not to burn the roux; if black spots appear, you will need to start over. When the roux has reached the desired color, add the onions and cook for 1 minute. Add the celery and cook for 30 seconds. Add the bell peppers, scrape the bottom of the pot, and cook for 1 minute. Add the garlic, cayenne, oregano, basil, thyme, and bay leaves, and season with more salt and pepper. Slowly add the broth, stirring constantly to avoid lumps of roux. Add the chicken and the sausage, stir, bring to a boil, then simmer for about 2 1/2 hours, skimming away any excess fat from the surface of the gumbo. When the meat falls off the bones, remove the skin and bones from the pot. If necessary to get the liquid to the desired consistency, add water or simmer to reduce.

Return to a boil and stir in fil powder. Stir vigorously to avoid clumping until the fil is dissolved. Adjust the salt and pepper, and finish with hot sauce to taste. Serve over boiled rice and garnish with green onions.