In a large saucepan, heat the butter or margarine and oil over medium heat. Add the chicken and brown lightly on each side. Once the chicken breasts are cooked (the juices should run clear) remove them from the pan and set aside.
Add the shallots and the chicken stock to the pan. Simmer for 3 minutes. Add the raspberry vinegar. Bring all to a boil and simmer, stirring, until the mixture thickens. Stir in the cream and return the chicken to the pan. Heat for 1 minute to warm the chicken, turning the chicken pieces to coat with the sauce. Season with salt and pepper to taste.
