Season the chicken thighs with 2 teaspoons of salt and 1 teaspoon black pepper.
In a heavy dutch oven over medium-high heat, brown the chicken thighs skin-side down until they release from the pan and are a nice golden brown, about 5-6 minutes. Remove from the pan.
Add the remaining oil and flour and, using a whisk, stir constantly, taking care not to allow any to splash and burn you, until the roux has turned dark brown (the color of a bar of Hershey's chocolate is about right), about 25 minutes.
Once the roux is the color of milk chocolate, add the trinity of onion, bell pepper, and celery, and stir once every 5 seconds for about a minute until the vegetables begin to soften and caramelize. The roux is very hot, so the vegetables are going to cook quickly. Don’t walk away! After a minute, add the garlic and bay leaves and cook for another 30 seconds, stirring frequently.
Deglaze the pot with the beer, scraping the bottom with a wooden spoon until all the browned bits are released. Stir constantly until it returns to a simmer.
Add the stock and continue stirring until it returns to a simmer. Add the remaining 1 teaspoon salt and 1 teaspoon black pepper and the cayenne.
Add the reserved chicken thighs (skin, bones, everything) and their fat and the sausage. Bring back to a bare simmer, being careful not to let it boil and not to let the roux scorch, reduce the heat to the lowest setting on your stove, and cover.
Simmer for 3 hours, stirring every 30 minutes, scraping the bottom each time. Your gumbo should begin to thicken, but not like gravy. If it starts getting too thick before the 3 hours are up and you have to hit it with a little water to thin it, do so.
Serve with rice. Garnish with sliced green onions. Top with Crystal Hot Sauce.