Prep your ingredients and set aside.
In a large pot, make a roux by combining the oil and flour. Cook over medium heat, stirring constantly, until the roux turns a rich brown (about 20-30 minutes).
Add the onions, bell pepper, and celery to the pot and sauté for 5-7 minutes, until softened. Add the garlic and cook for an additional 30 seconds until fragrant.
Slowly add the heated seafood stock, whisking to combine.
Add Cajun seasoning, bay leaves, granulated onion and garlic, and gumbo crabs. Stir well.
Bring to a boil, then reduce to a simmer for about an hour.
While the gumbo simmers, brown the sausage in a separate pan. Once browned, add it to the gumbo along with the Dungeness crab.
Cook for a few minutes, then add shrimp, green onions, parsley, and file powder. Cook for an additional 5-7 minutes until shrimp are pink and cooked through. Gumbo will also thicken slightly from file powder.
Taste and adjust seasoning as needed. Add water to adjust the consistency if desired.
Serve over rice and garnish with more green onion and parsley. Enjoy!