Peel and wash the potatoes, cover and cook in salted water for about 20 minutes.
In the meantime, remove any tendons and thin membranes from the liver. Wash the liver and pat dry. Peel onions and cut into thin rings. Wash apples, quarter them, remove seeds and cut into thin slices.
Turn the liver in 4-5 tablespoons of flour, tap lightly. Heat 2 tablespoons of butter in a large pan. Fry the liver in it over medium heat for 2-3 minutes on each side. Season with salt and pepper. Remove and keep warm.
Turn onions in 2 tablespoons of flour, tap lightly. Heat 2 tablespoons of butter in the frying fat and fry the onions in it until crispy, turning them over. Fry the apples briefly.
In the meantime drain the potatoes for the mashed potatoes. Heat the milk and add it to the potatoes with 3 tablespoons of butter. Mash with a potato masher. Season to taste with salt and nutmeg.
Arrange liver and mashed potatoes. Spread apples and onions with the frying fat on the liver.