Heat 1 1/4 cups oil in an 8-qt. Dutch oven until a deep-fry thermometer reads about 350°.
Season chicken with 1 tsp. black pepper and a generous amount of salt. Toss with 1/2 cup flour, coating lightly. Working in batches, fry chicken until golden. The chicken does not need to be entirely cooked through. Cook to golden and cook to render the chicken fat. Transfer to paper towels to drain.
Lower heat to medium-low and add remaining 1 1/2 cups flour to Dutch oven with oil. Whisk until smooth. Cook, whisking often, until color of roux is dark chocolate, 1–1 1/2 hours. You’ll want to stay on top of the roux, whisking very often the darker the roux gets. We want to get to a dark roux without burning it.
Add remaining 1 1/2 teaspoons black pepper, the chile and filé powders, cayenne, white pepper, paprika, garlic, celery, bell pepper, poblano, and onion to the dark roux. Cook until soft, 10–12 minutes. Add stock, increase heat to medium and bring to a boil.
Reduce heat to medium-low and cook the roux and vegetable mixture, stirring occasionally and skimming fat as needed, until slightly thickened, about 30 minutes.
Add reserved chicken pieces; cook until chicken is cooked through, about 45 minutes.
Add andouille and cook until chicken is falling off the bone, about an additional 1 hour.
Using tongs, transfer chicken to a cutting board and let cool slightly; shred, discarding skin and bones, and return to pot.
Heat remaining 2 tablespoons of oil in a 12″ skillet over medium-high. Cook okra until golden brown and slightly crisp, 8–10 minutes, then stir into gumbo; cook for 15 minutes. Garnish with scallions and serve with rice or cold potato salad.
I’ve made a roux GF by using sorghum flour. The texture is just a bit more grainy but it’s a fantastic option if you’re gluten-free!