Dry large pot with paper towels, then return pot to stovetop and increase heat under pot to medium. When pot is warm, add butter and let melt completely, stirring occasionally. Be careful not to burn or brown butter.
When butter is melted, sprinkle all-purpose flour into pot. Whisk butter and flour together until fully incorporated. Cook, whisking constantly to prevent sticking or burning, until roux develops rich, dark brown color, approximately 20 minutes. Be careful not to burn roux.
Once ideal color is achieved, add onion, celery, green bell pepper, and garlic to roux. Stir well with wooden spoon, fully incorporating veggies into roux. Cook, stirring occasionally, 15 minutes or until vegetables are tender.
While roux and vegetables cook, heat medium saucepan over medium-high heat. When saucepan is warm, add vegetable broth and bring liquid to gentle boil.
When vegetables are tender, pour vegetable broth into pot with roux. Stir to incorporate, using wooden spoon to scrape up any bits stuck to bottom of pot. Stir until roux and broth are fully combined.
Return beans to pot. Add Cajun seasoning packet, okra, bay leaves, thyme, hot sauce, 1 teaspoon filé powder, salt, and black pepper. Stir well to incorporate all ingredients and blend spices into liquid.
Reduce heat under pot to low. Cover pot with lid and let mixture simmer 1 hour, stirring occasionally.
After 1 hour, add Worcestershire sauce and remaining teaspoon filé powder. Stir to incorporate, then replace lid on pot. Continue simmering gumbo over low heat another 15 to 20 minutes, stirring occasionally. If desired, stir in 1 additional teaspoon filé powder after simmering.
When ready to serve, ladle gumbo into serving bowl(s) and top with ½ cup steamed white rice per bowl. Garnish with chopped scallions and serve warm with additional hot sauce if desired.