Heat the oil, remove the peel from the onions, cut into rings and sauté until translucent, douse with wine and sauté for 20 min until the wine has evaporated. Remove the onions and set aside.
Melt the butter, cut the liver into fine strips, add to the hot butter form and cook for 4 min, stirring throughout. Add the onions, heat until hot, season well with salt and freshly ground pepper. Sprinkle with parsley and bring to the table on the spot.