Clean, wash and cut the soup greens into large pieces. Peel 1 onion and lard with bay leaf and cloves. Boil the soup greens, larded onion, peppercorns and salt in 2 litres of water.
Wash the boiled beef and put it in the hot stock (meat must be covered). Bring to the boil, skim and cook at low to medium heat for about 2 1/2 hours. In the meantime, wash the potatoes and cook in plenty of water for about 20 minutes.
Add onions and bacon, fry briefly, season everything with salt and pepper. Set aside about 1/4 of the fried potatoes for garnishing.
Peel and finely grate the horseradish (approx. 2-3 tablespoons). Scrape or cut a few coarse curls for sprinkling with a knife or economy peeler. Melt 30 g fat in a pot and sauté the flour in it.
Gradually add 1/2 litre of sieved boiled beef stock while stirring, bring to the boil and simmer for 3-5 minutes. Squeeze lemon. Wash the apple and grate it in the lemon juice and turn it in.
Drain lemon juice, stir apple and finely grated horseradish into the sauce. Mix cream and egg yolk and stir into the sauce as well. Season to taste with salt and pepper. Heat 30 g fat in a frying pan, fry the potatoes briefly, then add the breadcrumbs and fry until golden brown while turning.
Season with salt and pepper. Heat the remaining fat and brown the onion in it. Add drained Brussels sprouts, season with nutmeg and toss. Cut the boiled beef into slices. Arrange on a plate with sprouts and sauce.
Sprinkle horseradish curls over the meat and garnish with apple wedges and lemon balm. Add remaining sauce and roast potatoes extra.