Heat the oil in a large frying pan over medium high heat. Add the chops to the pan and cook until golden, about 2 minutes per side. Reduce the heat to low, cover the pan and cook until tender but not dry, about 5 minutes per side. Season the chops with salt and pepper as you turn them. Transfer the chops to a warm plate and cover with foil.
Turn the heat to medium high and add the butter to the pan. Add the sage, onion and apple and cook, stirring occasionally, until soft and golden, about 5 minutes. Add the wine, cider or stock to the pan, bring to the boil and cook, stirring and scraping the bottom of the pan until slightly reduced, 2 minutes. Add salt and pepper to taste. Place the chops on warmed plates, top with apples and spoon over the pan juices. Serve at once with mashed potatoes.