Wash the potatoes and cook in boiling water for about 20 minutes. Then drain, rinse and peel. Cut potatoes into thin slices. Clean, peel and cut carrots into large pieces.
Peel onions, dice 1 finely, cut the rest into rings. Heat 3 tablespoons of oil in a pan. Fry the onion rings until golden brown. Take them out and let them drip off on kitchen paper. Wash the steaks, dab dry and season with salt and pepper.
Put the steaks into the hot frying fat and fry them for about 8 minutes, turning them over. Heat 1 tablespoon of oil in a second pan and fry the potatoes for about 10 minutes, turning them several times.
Season with salt and pepper. Heat the rest in a pot, sauté the onion cubes in it, add the carrots and season with salt, pepper and sugar. Deglaze with half of the stock and stew for about 10 minutes.
Wash the parsley, dab dry, pluck and cut into strips. Stir into the carrots. Take the steaks out and keep warm. Add the rest of the stock and cream. Let reduce to about half.
Stir in mustard and season with salt and pepper. Arrange the steaks with fried potatoes, carrots, fried onions and sauce on plates.