Season the pork chops with salt and pepper. Heat oil in a skillet over high heat. Cook chops until well browned, about 5 minutes. Turn chops and cook on the other side another 5 to 6 minutes. Remove to a warm serving platter.
Pour off most of the fat from the skillet. Add the onions and cook 3 minutes. Add 6 tablespoons of the wine and the vinegar. Stir with a wire whisk, scraping to dissolve brown bit stuck to skillet. Add chicken broth and tomato sauce, stirring to blend. Cook 5 minutes. Combine cornstarch with 1 tsp wine. Stir into sauce. Add mustard, any juices that have accumulated around the pork chops, salt and a generous amount of pepper. Heat sauce, but do not boil.