Lightly season the chicken with salt, pepper, and Creole seasoning.
Heat the oil over medium heat in a heavy-bottomed Dutch oven. Then cook the chicken until browned on both sides, remove it, and set it aside.
Brown the sausage, and set it aside.
Melt the butter with the oil in the same pan, then sprinkle in the flour and stir until smooth.
Cook on medium heat, stirring continuously, for about 20-30 minutes or until it turns a rich dark brown color, just like chocolate. Please don't walk away from the stove during this process, or it could burn. The time it takes is so worth it.
When you have achieved your desired color, remove the Dutch oven from the heat and let it cool slightly.
Return it to the heat. Add the onion, garlic, green pepper, and celery, and cook for 8-10 minutes, stirring frequently.
Then add chicken, sausage, crab legs, Creole seasoning, chicken bouillon or cubes, paprika, thyme, and bay leaves, and let it cook for 5 minutes.
Follow with the tomatoes (if using) and about 6 cups of chicken stock, then bring to a boil and simmer for 45-50 minutes. After that, add the shrimp and simmer for 5 more minutes.
Stir in filé powder, green onions, and parsley. Adjust the soup's thickness and flavor to preferences.