In a large stock pot, combine the clarified butter and flour. Cook over medium-high heat, stirring constantly, for about 20 minutes until the roux turns very dark brown almost black. (Don't be intimidated by the color of the roux, the darker it is the better).
add onion, carrot, and celery to roux and cook until tender.
Add garlic and cook briefly until fragrant.
Slowly add stock to roux in 3 stages, ensuring that the roux is completely smooth. Bring to a boil, then lower heat to a simmer.
Add cajun seasoning and file powder.
Add the sausage, chicken, shrimp, and allow it to cook until the shrimp just turns pink.