German "Tafelspitz" - Boiled beef with horseradish sauce

Besides the piece of meat you'll need:
- clarified butter
- 3 tsp salt (heaped)
- 8 black peppercorns
- 6 bay leaves
- 1 onion
- soup greens (celery, carrots, leek, parsley)
- 35 gram butter
- 20 gram flour (and about 1/2 l of the beef broth)
- 1 egg yolk
- 50-100 gram horseradish (depending on your taste, my mother would use more than 100 gram ;))