This is Mémère Matherne's Family recipe. The original Andouille sausage comes from the Longview Matherne Family Market. It's best made 24 hrs ahead so the flavors can mingle.
Chop onion, celery, green onions, and parsley. Slice sausage. Boil sausage in two quarts of water while making gumbo. Cut chicken into pieces and put aside.
Heat oil in a large soup pot. Wisk in flour and stir continuously for 10 minutes until chocolate colored or maybe like BBQ sauce. This is called the roux. Don't worry if it smells a touch burnt; that's what gives Gumbo its rich flavor.
Smother chicken in roux for 10 mins. Add onions and celery until wilted.
Add sausage and its water. Bring to a boil, and simmer for 50 minutes. Add Cajun seasonings to taste.
Turn off burner. Add filet. Cook 10 more minutes. Serve over rice.