When you get just a bit darker than peanut butter move your pot off the heat. Carefully add the onions and stir immediately. Remember, this is hot oil with flour in it. It will burn you badly. They don't call this cajun napalm for nothing. Be safe.
Something really cool happens when the onions go in. The roux almost immediately turns the colour of caramel. No clue why but it does. Darkens up quite a bit. No need for alarm.
Cook the onions over low heat for about 3 minutes. Add the spices and stir.
Mix in the celery and green pepper and cook until soft. This takes a few minutes. They are soft when they are soft.
Toss in the garlic. Cook for another 30 seconds, stirring constantly.
Add a half cup of warmed stock. Stir until combined. Add a second half cup and repeat. Now add a cup and stir. Add the remaining stock.
Simmer the gumbo base for 20 minutes.
While the gumbo base simmers slice the sausage.
After the gumbo base has simmered for 20 minutes mix in the chicken. Cook until barely done. This will take somewhere between 10-20 minutes depending on how big the pieces are and how much they were cooked in the oil. As always an instant read thermometer is your best bet. Shoot for 170F.
Add the sausage and simmer for an additional 3-5 minutes.
Just before serving mix in the pre-cooked shrimp to warm through.
Serve with rice (traditional) or with bread (not traditional but really good). Garnish with a bit of finely chopped green onion if desired.