Add the remaining 1 tablespoon of butter to the casserole and let melt. Increase the heat to moderately high and sprinkle 2 tablespoons of the flour over the mixture. Cook, stirring, until the flour begins to brown, about 3 minutes. Stir in the wine and bring to a boil. Add the chicken broth about 1/2 cup at a time, allowing the sauce to return to a boil and thicken between additions. Once all the broth has been added, stir in the chicken and season with salt and pepper. Keep the stew warm over moderately low heat.