Season the chicken with salt, black pepper, and one tablespoon of grapeseed oil. Broil it until slightly charred and golden, about 10 minutes, and set aside.
Heat a thick bottomed 4-quart Dutch oven over medium. Add the 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.
Add the garlic, celery, jalapeño, bell pepper, and onion and cook for one minute. Add the beer to deglaze, then add the stock, thyme, bay leaves, and 1 teaspoon black pepper. Stir slowly and continuously until the gumbo is back to a simmer, then add the chicken thighs and the sausage. Bring to a simmer and cover. Cook, stirring occasionally, for 3 hours. Gumbo should thick but not like gravy. Season with cayenne and serve with cooked rice. Top with scallions and enjoy!