Spray a large non-stick skillet with oil and heat over medium heat. Season the pork with salt and pepper and add to the skillet. Cook the pork chops under the undersides are golden brown, takes about three minutes. Flip the pork and cook it until the other side is golden brown too, and the meat feels firm when pressed in the thickest part with a fingertip. Transfer to a plate. Whisk the cornstarch into the broth. Add the milk and mustard and whisk again, set aside. Melt the butter in the skillet over medium heat. Add the shallots or onion and cook, stirring often, until it is tender. Whisk the broth again, and then pour in the skillet and bring to a boil. Return the pork and any juices on the plate to the skillet and cook, turning occasionally, until the sauce thickens. Transfer the pork to plates and cut each chop in half. Pour the sauce over the pork chops and sprinkle with rosemary. Serve hot.