Heat the oil and flour in a Dutch oven or other large pot over medium heat.
Stir or whisk continuously until a chocolate brown roux forms (medium brown color). This will take about 15-20 minutes.
Add the andouille sausage, green pepper and onion. Stir and let cook for 5 minutes, stirring regularly.
Add the tomatoes and cook another 2-3 minutes.
Add the seasonings (Cajun seasoning, bay leaf, Worcestershire sauce, brown sugar) and mix in.
Slowly pour in the warmed stock, whisking constantly to ensure the roux doesn't break.
Add the okra and simmer for 45 minutes.
Add additional Cajun seasoning or salt to taste.
Add the crawfish and simmer another 5-10 minutes.
Serve over white rice garnished with green onions.
Notes
When making the roux, be sure to stir it constantly so it doesn’t burn or break. (Learn more about how to make a roux, including how you can try to fix a broken roux).
To prevent lumps from forming in the gumbo, use warmed stock and stir it in slowly. I usually add one cup at a time.
If the gumbo is too thick, you can just add more seafood broth.
If you don’t have seafood broth, you can use chicken broth like this homemade crockpot chicken broth.
To control the saltiness of the gumbo, I prefer to use homemade or low sodium broths.
Be careful not to overcook the gumbo as the crawfish may get tough and the veggies too soft.
For extra heat, just add more Cajun seasoning or a little cayenne pepper.
For the best flavor, let the gumbo sit in the fridge overnight before serving.