Serves 8-10, with rice.
3 Tbsp + 3/4 cup canola oil
2-1/2 lbs boneless, skinless chicken thighs, trimmed of excess fat
Kosher salt and fresh black pepper
1 cup all-purpose unbleached flour
1 large bunch celery, cleaned and trimmed, finely chopped in a food processor (5 cups)
4 large onions, peeled and trimmed, finely chopped in a food processor (8 cups)
4 green or red bell peppers, finely chopped in a food processor
2 Tbsp minced garlic
1 tsp cayenne pepper
3/4 tsp dried oregano
3/4 tsp dried thyme
4 bay leaves
6 cups chicken stock, homemade or low-sodium
1-1/2 lb sausage: beef hot links or chicken andouille
1 Tbsp filé powder
6 cups cooked long-grain white rice
Chopped scallions for garnish (optional)
In a heavy Dutch oven or large soup pot (5-6 quarts), heat 3 tablespoons of the oil over high heat until almost smoking. Place 1/4 cup of the four in a bowl, and lightly dredge the chicken pieces in the flour. Shake off the excess, then place the chicken in the hot oil. Sear until golden brown, turning once. It should take 6-8 minutes to brown the chicken. Remove, and set aside.
Put the pot back on the stove over medium heat, and add the celery, onion and bell peppers. Cook, stirring occasionally, until the vegetables are soft (10-12 minutes). Remove the vegetables from the pot and set aside. Wipe the pot with a paper towel, but do not wash. It's fine if a few bits of vegetable are stuck to the pan, but try to get it as clean as you can.
Heat the remaining 3/4 cup of oil in the pot over medium heat. Stir in the remaining 3/4 cup of flour, and stir constantly with a wooden spoon until the mixture (this is the roux) is the color of medium-dark chocolate. This is going to take at least 20 minutes, and probably longer. Go slowly, stir thoroughly, making sure to break up any lumps as you go. (To learn a bit more about dark brown roux, watch Chef Paul Prudhomme in action.)
When the roux is a nice mahogany brown color, stir in the cooked vegetables, garlic, cayenne, oregano, thyme, and bay leaves. Stir until everything is combined (be sure to scrape up any bits stuck to the bottom of the pot). Cook for 3-5 minutes, then season with salt and pepper.
Pour in the chicken stock and water, and add the sausage and chicken. Bring everything to the simmer, and skim off any excess fat that comes to the surface. Reduce heat and simmer, uncovered, for 2-1/2 hours, skimming any foam or fat off the surface. Stir occasionally to keep the stew from sticking as the liquid reduces.
After 2-1/2 hours, add the filé powder, and stir vigorously as the stew thickens. Taste, and add salt and pepper to taste. Remove the bay leaves.
Place some cooked rice in each bowl, and ladle the gumbo on top. Garnish with scallions, if desired, and serve hot.