The base of gumbo is a roux. Every single recipe I found suggests you need to drink whilst making the roux, so here goes. Fry some chicken thighs, till brown and the sausage, pour the fat into a big old pan, add butter & melt it and then add flour, turn the heat low & stir and scrape and stir & scrape. Keep stirring & scraping till the roux is Milk chocolatey coloured (about 2 beers of time, or 45 minutes for the more scientifically minded).
Once you've a lovely roux, throw in the trinity veggies and any others you are using (I know Okra should go in at this point, but I'm not that keen, even if its where gumbo gets its name) and soften them. Add seasonings & spices. Then add your stock and your meat (Sausage & chicken) and let it bubble over a low heat for hours. I reduced my gumbo a little too much at the end, so it was thicker than most. Serve with white rice, a sprinkle of filé and some buttery bread.
Maybe not the most authentic gumbo as I amalgamated 3 recipes and information from an ex-NOLA resident, but it was damn tasty and next time there is cheap shellfish going I'll be making another.
The recipes are here
and the highly recommended baconconcentrate's gumbo-shops recipe