Boiled Beef with Wild Garlic Sauce

For the beef: Put soup bones in a pot, cover with water, bring to a boil, then pour into a colander. Return soup bones to the pot, add more water and boil again. Rinse beef and add to pot. Simmer beef for about 2 hours and skim off foam throughout. 

Peel and chop parsnips and carrots. Rinse and chop leeks and celery. 

Peel onion, cut in half and brown, cut-side down, in a hot, dry pan. Add vegetables, onion halves, spices and peppercorns to beef and simmer for about 1 hour more. 

For the sauce: Rinse and mince wild garlic. Peel and dice onion. Heat butter in a pan and cook onion. Add flour, cook briefly, then and deglaze with milk, broth and cream. Add wild garlic and bring sauce to a boil. Season with salt and pepper. Whisk in some yolk and simmer but do not boil. Stir in chives and season to taste.