Peel and wash 2 onions and 2 carrots each and cut them into large pieces. In a large pot without fat roast briefly. Add approx. 2 l water, peppercorns and 1 tsp salt and bring to the boil. Wash and add the boiled beef, cover and simmer for about 1 1/2 hours.
Skim off the foam from time to time.
Clean or peel and wash the rest of the vegetables. Cut leek into thin rings, carrots into thin slices. Peel remaining onions and cut into rings. Peel and wash potatoes and cut into small cubes.
Melt 2 tablespoons of butter in a large frying pan. Stir-fry the potatoes and onions for 12-15 minutes until crispy. Season with salt and pepper.
Lift out the boiled fillet of beef. Remove approx. 200 ml of the meat stock and sieve. Cook the carrots and leek for 8-10 minutes. Peel horseradish and grate coarsely. Mix immediately with lemon juice.
Cut the boiled fillet of beef into slices of about 1 1/2 cm thick. Remove the potatoes. Heat 2 tablespoons of butter in the frying fat. Fry meat slices in it in 2-3 portions on each side for 1-2 minutes. Arrange everything and sprinkle with horseradish.