1 tablespoon plus 1/2 cup vegetable oil
1 pound smoked sausage, such as andouille or kielbasa, cut crosswise 1/2-inch thick pieces
4 pounds chicken thighs, skin removed
1 tablespoon Creole seasoning
1 cup all-purpose flour
2 cups chopped onions
1 cup chopped celery
1 cup chopped bell peppers
1 teaspoon salt
1/4 teaspoon cayenne
3 bay leaves
9 cups chicken stock or canned low-sodium chicken broth
1/2 cup chopped green onions
2 tablespoons chopped parsley leaves
1 tablespoon file powder
In a large enameled cast iron Dutch oven or large pot, heat 1 tablespoon of the vegetable oil over medium-high heat. Add the sausage and cook until well browned, about 8 minutes. Remove the sausage with a slotted spoon and drain on paper towels. Set aside.
Season the chicken with the Creole seasoning and add in batches to the fat remaining in the pan. Cook over medium-high heat until well browned, 5 to 6 minutes. Remove the chicken from the pan, let cool, and then refrigerate until ready to use.
Combine the remaining 1/2 cup oil and the flour in the same Dutch oven over medium heat. Cook, stirring slowly and constantly for 20 to 25 minutes, to make a dark brown roux, the color of chocolate.
Add the onions, celery, and bell peppers and cook, stirring, until wilted, 4 to 5 minutes. Add the reserved sausage, salt, cayenne, and bay leaves, stir, and cook for 2 minutes. Stirring, slowly add the chicken stock, and cook, stirring, until well combined. Bring the mixture to a boil. Reduce the heat to medium-low and cook, uncovered and stirring occasionally, for 1 hour.
Add the reserved chicken to the pot and simmer for 1 1/2 hours, skimming off any fat that rises to the surface.
Remove the pot from the heat. Using a slotted spoon, remove the chicken thighs from the gumbo and place on a cutting board to cool slightly. Remove and discard the bay leaves. Pull the chicken meat from the bones and shred, discarding the bones and skin. Return the meat to the gumbo and stir in the green onions, parsley, and file powder.
Serve over white rice.