Season the chicken all over with the Essence and 1/2 teaspoon of the salt. 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.
Heat 1 teaspoon of the olive oil in a 10-to 12-inch flameproof casserole or saute pan over medium-high heat. Add 2 tablespoons of the butter, and when it has melted, place the chicken, skin side down, in the pan. Brown for 2 minutes on each side. Remove the chicken from the pan and set aside.
Add the remaining 1 tablespoon butter to the pan, and when it has melted, add the onions, garlic, thyme bundle or rosemary sprigs, remaining 1/2 teaspoon salt, and the black pepper. Cook, stirring as needed, until the onions are translucent, about 4 minutes. Sprinkle the 1 tablespoon 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, skin side down, 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 15 minutes.
Uncover the pan, stir the bottom of the pan to prevent scorching, and turn the chicken skin side up. Cover the pan, and simmer for 20 minutes longer.
Stir the bottom of the pan a final time, re-cover, and simmer for 20 more minutes.
Remove the pan from the heat and discard the herb bundle or rosemary sprigs. Transfer the chicken to a serving platter. Add the parsley to the sauce, stir to combine, and then spoon the sauce over the chicken. Serve with steamed white rice.
Yields 4-6 servings