Place the flour and oil in a large well insulated soup pot over medium heat.
Stir every 45 seconds as the roux turns blond, then brown then dark brown.
When very dark brown and aromatic, add the vegetables, andouille sausage, herbs, spices and garlic.
Saute until onions are glassy, add the tomatoes and stir.
Add the stock and worcestshire.
Bring mixture to a boil, reduce heat to maintain a simmer, and simmer for 1 hour.
Add the seafood and continue cooking for 5 minutes.
Season with salt and pepper and serve, passing crusty bread at the table.