Gather the ingredients.
Melt duck fat in a large pot on medium heat, then whisk in the flour. Continue cooking on medium heat, whisking frequently, until the roux is dark brown, the color of milk chocolate, but not black or burned. This will take about 18 to 20 minutes, depending on your flame.
When you reach the desired color, immediately add the trinity—the diced onions, green pepper, and celery—plus the garlic. Using a wooden spoon, stir the trinity into the roux, making sure it is evenly distributed, season with a few pinches of salt and black pepper. The roux will look dry at first, cook the trinity in the roux, stirring frequently, until the vegetables begin to soften and the roux looks moist, about 10 minutes.
Gradually stir in the chicken stock, dissolving the roux and preventing lumps, turn the heat up to medium-high and bring the pot to a boil.
While you’re waiting for the pot to boil, heat a large sauté pan over medium-high heat. Season the chicken thighs with salt and pepper and add the tablespoon of oil to the pan.
Place the thighs skin-side down in the pan and sear until the skin is a deep golden brown, 7 to 10 minutes. Flip the thighs and sear the bone side for 2 to 3 minutes.
Remove the thighs from the pan and add to the pot, leaving the fat in the pan and keeping the sauté pan on medium-high heat.
Add the sliced andouille to the pan and cook, stirring occasionally, until the sausage is browned in places and the edges are curling, about 5 to 7 minutes.
Turn off the heat, then use a spatula to scrape the andouille and any accumulated fat into the pot. Add the crab knuckle and give the contents a good stir to combine. If the ingredients are not covered by the stock, add 1 to 2 cups water to just cover.
Raise the heat under the pot and bring its contents to a full boil. Then reduce the heat to a simmer and add the bay leaves and dried thyme. Skim any fat and foam that accumulates on the surface and simmer for one hour.
Carefully remove the chicken thighs to a large plate. When the chicken has cooled a bit, discard the skin, bones, and cartilage, shred the meat, and return it to the simmering pot.
Add the okra and Worcestershire sauce and continue simmering the gumbo for another hour on low heat, stirring occasionally to make sure it’s not sticking or burning.
Remove the crab knuckle and pick out any remaining meat. Stir the crab meat into the gumbo to distribute and then discard the shell. Stir in the filé powder, taste, and adjust the seasoning with salt and pepper. Simmer for another 5 minutes, then turn off the heat.
To serve, place about 1/2 cup cooked rice into serving bowls and ladle the gumbo on top of the rice. Garnish with sliced scallions and add a few dashes of hot sauce to taste.