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 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.