In a large 8 qt, heavy-bottomed pot, brown andouille sausage. Once browned on both sides remove sausage and set aside.
Add vegetable oil to the pot, over medium heat. Add the flour and stir continuously to make a roux. Cook the roux, stirring frequently with a wooden spoon, until it reaches a dark brown color, like milk chocolate, about 20-30 minutes.
Add the onions, bell peppers, and celery to the roux and stir. Cook the vegetables for 5 minutes, then add the garlic and cook for another 30 seconds.
Add the andouille sausage back to the pot. Cook for an additional 5 minutes, stirring occasionally.
Pour in seafood stock and bring to a boil. Lower the heat to medium low and add bay leaf, thyme, salt, cayenne, and Bayou City Seasonings.
Continue to simmer the gumbo for 45 mins, skimming the foam and any oil that rises to the surface.
stir in gumbo file and continue to simmer for 15 more minutes
Add the green onion, crab legs, and shrimp to the pot. Cook for 5-7 minutes, or until the shrimp are pink and opaque.
Taste the gumbo and season if necessary.
Garnish with the parsley and green onions and serve in shallow bowls over white rice.
