Gumbo is also one of those dishes, like chili, that I don't really use a recipe for. There are a few things I think are required to make good gumbo, and then the rest is all flexible.
Here are the basic steps:
1. Make a roux.
2. Add the Holy Trinity, okra, and meats to the roux and fry them in it a bit.
3. Add broth and Cajun spices.
4. Simmer until done.
OK, let's make this a little less vague.
Roux is made by mixing a paste of roughly equal parts of flour and fat (I usually prefer putting a little more flour than fat in mine to make a thicker paste) and cooking it over low heat until it is rich brown. Lighter rouxs are used in a variety of sauces to thicken them, but when you cook roux until it almost burns but not quite, it toasts the flour creating a delicious nutty flavor. To make dark roux, you have to stand over the pot and stir and stir over low heat until it gets the right color and aroma (you will notice when it starts smelling delicious). Stir constantly so the flour on the bottom doesn't burn. I actually rush my roux a little bit at the beginning and have the heat up on medium, but as soon as the flour starts to brown, you really have to do it over low heat so you don't cross the line from toasty brown to black. If you start getting black flakes in it, you've burned it and will have to start over.
I have heard that it's possible to make roux in the oven, though I haven't tried it yet. Maybe next time.
It's really not that hard. It just takes patience. It's probably the most tedious part of gumbo making. For a big pot of gumbo, I use about a quarter cup each of fat and flour. For a smaller pot, two tablespoons of each should work. The fat can be butter, olive oil, bacon grease, chicken fat or some combination of those. Pick something you think would go well with the rest of your ingredients.
Once the roux is done, everything else is just thrown in and mixed together.
The meat you use in gumbo is the most flexible part. Sausage is good. I always put sausage in my gumbo along with whatever other meat I have chosen because it gives that great smoky flavor. I let it brown a bit in the roux with the vegetables. If you can find andouille sausage, that would be the most authentic, but I often have to settle for regular smoked summer sausage (if you can find a spicy kind, that's even better). I've heard of ham being used also, but haven't tried it myself.
Chicken is also good and a very common ingredient. I usually use chicken that's already been cooked, like leftovers from a roasted chicken (hmm, I wonder if leftover Thanksgiving turkey would work as well). You can use chunks of raw chicken, like cubed chicken breast or thighs. Raw chicken should be added with the raw vegetables so it can cook in the roux a bit, but it's a good idea to wait to add cooked chicken until after you add the broth, since you're just reheating it and don't want to overcook it.
And of course there's seafood. Shrimp is always a favorite, and I've also used catfish nuggets. Crab, scallops, oysters, and crawfish can also be put in, though I've never tried it before. Since seafood cooks so quickly, it should be added towards the end, at the same time you add cooked chicken, so it can cook only briefly.
I use a pre-made Cajun seasoning mix, but you can also make your own. Cajun seasoning usually has salt, black pepper, Cayenne pepper, garlic, thyme, and maybe some other things. They vary in how hot and how salty they are, and people vary in how hot or salty they like their food, so I'm going to have to tell you to just season to taste here. Fortunately, once any raw meats you added are cooked, you can taste your gumbo and add more seasoning if you think it needs it (but remember you can add but you can't take out). I usually make my gumbo a little milder than I prefer, and then pass some Louisiana hot sauce around at the table for people who like it hotter to add to their portions.
Simmer the gumbo until everything is cooked and the roux and spices are incorporated into the broth, but don't let the vegetables get too mushy. Oh, and you were cooking a pot of rice to go with it, weren't you?
Serve over rice (white or brown are both good), with some crusty French bread on the side, and a sweet white wine. Cajun food is influenced by French food, which is why I accompany it with French bread and a sweet wine that would go with spicy food. Maybe it's because I grew up watching Justin Wilson on PBS, and he always drank wine. But beer is good too, and I know some people who eat cornbread with gumbo (but I prefer beer and cornbread with chili).
Now that is some serious comfort food for when it's starting to get a little cold outside, but you still have lots of okra and bell peppers from the garden to use up.