Add the oil and then stir in the flour, a little at a time. Cook, stirring constantly, until the roux is the color of a penny. Do not rush, and do this over medium to medium-low heat.
In a Dutch oven, cook the bacon and sausage until the bacon is crisp and the fat has rendered out. Spoon out all but about 1 tablespoon of the fat.
Add the onion, peppers and celery, and sweat over medium-low heat until the vegetables are softened but not browned. Regulate the heat so you hear a gentle sizzle, not an angry sizzle or sputtering/popping.
Add salt and pepper, to taste, the pepper flake, thyme and bay leaves.
Once the vegetables are translucent, add the roux, and stir until well combined.
Pour in the beer and bring to a boil. Reduce by about half, turn down the heat and add 2 teaspoons filé powder, the tomatoes and chicken broth.
Bring to a boil, then turn down the heat and simmer for about an hour. Taste, and adjust seasonings.
Add the chicken and okra and simmer for an additional thirty minutes.
Stir in the remaining 2 teaspoons of filé powder and serve over cooked rice.
Notes
Like most braises and stews, gumbo is even better the next day. If not serving immediately, omit the last 2 teaspoons of filé powder and add it after you reheat the gumbo the next day.