Peel, wash and halve the potatoes and boil them in salted water for about 20 minutes. Melt 20 g fat in a pot, sauté the flour in it. Stir in broth and 1/8 litre milk, bring to the boil. Season to taste with mustard. Cut the cress from the bed and add it to the sauce, except for something to garnish.
Boil up about 1 litre of salted water and vinegar. Beat the eggs one by one in a ladle and carefully slide them into the vinegar water. Cook 4-5 at low heat. Remove with a skimmer, dip briefly in cold water, drain and keep warm. Drain the potatoes, add 1/8 litre milk and 10 g fat. Season with salt and mash to mashed potatoes. Peel onion and cut into rings. Heat oil in a pan. Brown onion rings in it, take out.
Season with salt and mash to mashed potatoes. Peel onion and cut into rings. Heat oil in a pan. Brown onion rings in it, take out. Garnish mashed potatoes with onion rings, arrange poached eggs and mustard sauce on plates. Sprinkle the rest of the cress on top