1/2 cup vegetable oil
1/2 cup all-purpose flour
1 large onion, diced
1/2 cup chopped fresh parsley
1/2 cup chopped celery
1/2 cup chopped green bell pepper
1/2 cup chopped red bell pepper
1/2 cup sliced scallion
6 cloves minced garlic
4 cups chicken broth
1 teaspoon salt
1 teaspoon creole seasoning (Tony Chachere’s)
2 lbs any combo of sausage or 2 lbs shrimp or 2 lbs chicken (etc.)

1  In a large stockpot combine oil and flour and cook over medium-high heat about 15 minutes or until it turns very dark brown, almost between brown and black.
2  You will have to stir almost constantly.
3  This is called the roux.
4  Add onions, parsley, celery, bell peppers, scallions and garlic and cook about 10 more minutes or until vegetables are tender, stirring regularly.
5  Add broth, salt, and creole seasoning.
6  (If you like you may also add a 10 oz package of frozen okra at this point, but I despise the stuff).
7  Cover pot and simmer 15 minutes stirring occasionally.
8 Add your chosen combination of meat at this point and simmer an additional 10 minutes (if using whole pieces of crab like claws, or blue crab halves cook a little longer to ensure they’re cooked all the way.).
9  Ladle over steamed white rice.

source:    http://www.food.com/recipe/gumbo-32042