Cut apples into 1/2 inch thick rings. Melt butter in heavy skillet and lightly fry bacon until golden. Remove and drain on paper towels. Keep warm. Fry the onions rings in the remaining fat until soft. Add the apples. Cover and simmer for 5 to 10 minutes, shaking the pan from time to time to prevent sticking. Return the bacon to the pan and heat through. Season with pepper, sprinkle with parsley and serve.