For the Roux: A large, heavy pot is a must - the heavier the better. Patience is a must - the more the better.
Mix flour and oil until thoroughly blended before heating. Turn heat on medium-low and immediately begin stirring. Allow roux to brown slowly, stirring constantly.For the Gumbo:
When roux is dark brown, add the chopped vegetables. Increase heat to medium and stir until onions are translucent. Add seasonings, stirring to blend. Add sausage and chicken, stirring until evenly browned.
Slowly add heated chicken stock, stirring constantly. Continue stirring until gumbo comes to a simmer. Simmer 1 hour, stirring often and reducing heat if necessary to prevent sticking. Add salt to taste.
You can adjust the final thickness of the gumbo with filé powder, or pass it at the table as a traditional accompaniment.