In a large skillet, heat olive oil over medium heat. Add sliced andouille sausage and cook until lightly browned, about 5 minutes. Add the diced onion, green bell pepper, and red bell pepper. Sauté until translucent, about 8–10 minutes. Add the minced garlic and cook for another 2 minutes. Remove the mixture from the pan and set aside.

In a large pot or Dutch oven, add the flour to the dry surface and toast over medium heat, stirring constantly until it turns light brown. Add butter and continue stirring until the mixture becomes a deep chocolate-brown color. This is your roux — the foundation of gumbo’s rich, smoky flavor.

Add the cooked sausage and vegetable mixture back into the pot with the roux. Stir well to coat everything evenly. Add the salt, black pepper, paprika, cayenne, thyme, oregano, garlic powder, and onion powder. Stir to bloom the spices and release their aroma.

Pour in the chicken stock (and oyster liquor if using) along with the bay leaf. Stir well and bring to a gentle boil. Reduce heat to low and let simmer uncovered for 25–30 minutes, stirring occasionally as the flavors meld and the gumbo thickens.

Season the shrimp with the same spice blend and add them to the gumbo during the final 5–7 minutes of cooking. Simmer just until the shrimp are pink and tender — avoid overcooking.

Remove the bay leaf. Ladle the gumbo over bowls of cooked white rice and garnish with sliced green onions. For an authentic Creole touch, dust each serving lightly with filé powder before serving.