Brown the Sausage: Add the sliced andouille sausage (1 pound) to a large heavy-bottomed pot or Dutch oven over medium-high heat. Cook until well caramelized and the fat has rendered. Remove to a plate and set aside.
Brown the Chicken: Season the chicken thighs (6) lightly with salt and pepper. Brown them in the same pot, turning to get good color on all sides. Remove and set aside with the sausage.
Cook the Trinity: Add the onion (1), bell pepper (1), and celery (2 ribs) to the pot. Spread them out and cook over medium heat, scraping up the flavorful browned bits from the bottom of the pot. Let the vegetables soften and sweat, about 8–10 minutes.
Add half of the minced garlic (3 cloves), cook 30 seconds more, then remove the vegetables to a plate.
Make the Roux: Wipe the pot clean. Add the oil (1 cup) and flour (1 cup) and cook over medium-low heat, stirring constantly. Do not walk away.
The roux will gradually darken through several stages. Continue cooking and stirring until it reaches a deep chocolate-brown color, similar to dark milk chocolate. This can take 25–40 minutes. If it smells burned or turns black, discard and start over.
Bloom the Spices: Once the roux reaches the correct color, reduce the heat to low. Stir in: smoked paprika (2 teaspoons), garlic powder (1 teaspoon), onion powder (1 teaspoon), cayenne pepper (1/2 teaspoon).
Cook for 30–45 seconds, stirring constantly, just until fragrant.
Build the Gumbo: Return the sausage, chicken, and cooked trinity to the pot. Add the remaining minced garlic (3 cloves), oregano (1 teaspoon), thyme (1 teaspoon), basil (1/2 teaspoon), bay leaves (2), salt (2 teaspoons), and black pepper (1 teaspoon). Stir well to coat everything in the roux.
Slowly pour in the chicken broth (8 cups) while stirring. Add the Better Than Bouillon (1 heaping teaspoon), if using. Bring the gumbo just to a gentle simmer.
Reduce heat to low and simmer uncovered for about 2 hours, stirring occasionally. The chicken should become very tender and begin pulling away from the bone.
Shred the Chicken: Carefully remove the chicken thighs to a plate. Discard the bones and shred the meat. Return the shredded chicken to the pot and stir to combine.
Finish with Filé (Optional): Turn off the heat. If using, sprinkle in gumbo filé powder a little at a time, stirring, until the gumbo thickens slightly to your liking. Do not boil after adding filé, or it can turn stringy.
Serve: Ladle the gumbo over hot white rice. Garnish with sliced green onions. Serve with potato salad on the side, if desired.