In a large frying pan, heat the oil and butter. Add the onions and parsley, mix well and simmer over very low heat, stirring occasionally, for 40 minutes, or until the onions are soft and translucent but not colored. At the first sign of browning, add the stock and vinegar. Increase the heat. Add the liver and saute briskly for 4 to 5 minutes, or until the slices are browned on both sides. Season with salt and pepper. Turn out on to a heated platter and serve immediately.{$7e}(Original recipe for 4)
