Mix the oil and flour together really well in a 6 - quart pot on the stove. Turn heat to a medium-high setting (about a 7 on a scale from 1 to 10, 1 being the lowest temperature and 10 being the highest). Cook about 15 – 20 minutes until it is practically the color of chocolate pudding, stirring constantly and removing from heat as needed to prevent over-smoking (which means it’s burning). It will start to get loose when it is too dark – that indicates that the roux is losing its thickening power, and you don’t want that!
Next, add the onion, celery, bell pepper, garlic and the okra to the roux; mix well. Cook the resulting mixture over low heat, stirring occasionally so as not to burn it, until the onions are soft and translucent and the mixture is reduced down a little. I cover the pot and "sweat" the vegetables in the roux so that their moisture is rendered in the pot.
Add the tomatoes and their liquid gradually with the chicken/ham broth. Add the rest of the ingredients (except the rice); cover and simmer on very low heat (just so it “percolates” in the pot - you might have to cock the lid a little) at least 1 hour, but preferably up to 2½ hours, stirring occasionally.
Don't forget to take out the bay leaves before serving!
Serve in wide-rimmed bowls topped with about a third-cup of cooked, white rice ladled in the center of it. We also traditionally sprinkle a little filé powder over the gumbo at the table.