Season pork chops generously with salt and pepper. Heat oil in heavy large skillet over medium-high heat. Add pork to skillet and cook until brown and cooked through, about 5 minutes per side. Transfer pork to platter and tent with foil to keep warm.
Drain off all but 1 tablespoon drippings from skillet. Add butter to skillet and melt over medium heat. Add onion and apple to skillet and saute until onion is almost soft, about 5 minutes. Mix in cider, vinegar and bay leaf. Cover skillet and cook until onions and apples are tender, about 10 minutes. Discard bay leaf. Add any accumulated juices from pork chop platter to skillet. Increase heat and cook until sauce thickens slightly, about 3 minutes. Spoon sauce over pork chops and serve.