Melt butter in skillet with drippings. Mix brown sugar into drippings and stir until smooth. Add maple flavoring. Layer in 13 x 9 inch baking dish: pork chops, onions, yams and then apples. Pour brown sugar mixture over all and sprinkle with nuts. Cover with foil and bake at 350 degrees for 1 hour or until vegetables and chops are tender. Remove foil and bake another 15 minutes.