Wash meat for the broth. Halve the onion crosswise and fry the cut surfaces in a pan without fat. Peel or clean the soup greens, wash and roughly dice them. Put meat and soup vegetables into the pot, cover with salted water.
Wash the herbs and shake dry. Add bay leaf, thyme, rosemary and 4 sage leaves to the meat. Bring to the boil and simmer for about 2 hours. In the meantime, skim off boiling egg white foam with a skimmer.
Remove meat from the broth, remove from the bone and cut into cubes. Pour stock through a fine sieve. Coarsely grate the cheese and distribute evenly on the slices of bread. Bake in a preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for approx. 5 minutes.
Peel the garlic and cut into fine slices. Heat the oil in a pot. Roast the garlic for about 2 minutes while turning. Measure the stock and if necessary fill up to 1 litre with water. Pour into the pot and bring to the boil.
Take the pot off the stove. Cut 4 sage leaves into fine strips. Whisk egg yolk and cream. Pour into the hot, non-boiling soup while stirring. Add sage and meat. Season to taste with salt and pepper.
Possibly put bread on top of the soup.