Preheat the oven to 400? F. Season the chicken with salt and pepper to taste, and dip all sides of each breast in the flour. Shake off any excess flour. In a large skillet, heat the olive oil. When the oil is hot, add the chicken, skin side down, and cook over medium-high heat, for about 4 minutes on each side to brown. Transfer the chicken to a baking dish and bake for 20 to 25 minutes or until cooked through. TO MAKE THE SAUCE: Discard all but 2 tablespoons of the oil from the skillet in which the chicken was cooked. Heat this oil and saute the onions, over low heat, for about 5 minutes or until soft. When the onions are tender, add the vinegar, Port and white wine and boil the liquid down until only half remains. Add the chicken stock and heavy cream and bring to a simmer. Reduce the sauce to thicken it slightly. Dissolve the cornstarch in the water and add it to the sauce. Bring the liquid to a boil and simmer over low heat for a minute. Season the sauce with salt and pepper to taste and remove it from the heat. When the chicken is done, over low heat bring the sauce back to a simmer, but do not boil. Stir the walnuts into the sauce and spoon it over the chicken. Serve immediately. Per serving: 2619 Calories (kcal); 191g Total Fat; (67% calories from fat); 150g Protein; 54g Carbohydrate; 480mg Cholesterol; 2018mg Sodium Food Exchanges: 2 1/2 Grain(Starch); 20 1/2 Lean Meat; 1 Vegetable; 0 Fruit; 25 1/2 Fat; 0 Other Carbohydrates Converted by MM_Buster v2.0n.