Preheat oven to 400 degrees F. Sprinkle chops with salt and pepper. Coat the bottom of a large, ovenproof frying pan with the oil and heat over med.-high heat. Add the chops and sear them until both sides are golden brown, about 2 minutes per side. Place the pan in the oven and roast until an instant-read thermometer registers 130 degrees F., or the meat is deep pink near the bone for med. rare, 6-8 minutes. Transfer to a platter and cover with aluminum foil and set aside.
Drain off all but 1 tablespoons of the drippings from the frying pan. Add the shallots and garlic and saute, stirring frequently for 3-4 minutes. Add the Port and stock and bring to a boil over high heat. Cook until reduced b half, about 5 minutes. Reduce the heat to medium. Whisk in the mustard and then the butter. When the butter has melted and the sauce is smoot, season with salt and pepper. Slice the chops in to individual pieces, spoon on the sauce, and serve immediately.