1. Season the chicken all over with the seasoning of your choice. Place the 1 /2 cup flour in a small bowl, and quickly dredge both sides of each thigh in the flour, shaking to remove any excess. Set aside.
2. Heat 1 tablespoon of the olive oil in a 10- to 12-inch flameproof Dutch oven or sauté pan over medium-high heat. Add 2 tablespoons of the butter, and when it has melted, place the chicken in the pan. Brown for 2 minutes on each side. Remove the chicken from the pan and set aside.
3. Add the remaining 1 tablespoon butter to the pan, and when it has melted, add the onions, garlic, thyme, rosemary, and sage, remaining a pinch of salt, and the black pepper. Cook, stirring as needed, until the onions are translucent, about 4 minutes. Sprinkle the 2 tablespoons dredging flour over the onions and cook for 2 minutes longer. Then whisk in the chicken stock and increase the heat to high. Return the chicken to the pan, and bring the stock to a boil. Reduce the heat to medium-low, cover the pan with a heavy, tight-fitting lid, and simmer for 20 minutes.
Uncover the pan, stir the bottom of the pan to prevent scorching, and turn the chicken over.
4. Cover the pan, and simmer for 20 minutes longer. Meanwhile, add 2 ½ tablespoons flour to reserved chicken broth and whisk or shake until all lumps are gone. Set aside.
5. Transfer the chicken to a serving platter and stir the bottom of the pan. Add the reserved broth mixture to the sauce in the pan; stir to combine, and then spoon the sauce over the