Put the bones in a saucepan with the meat, onions, carrot and water. Add salt and bring everything to a boil. Skim off the foam that forms with a trowel. Cover the saucepan and let the soup simmer for about 2 hours until the meat is very soft. Then pour the broth through a sieve into another saucepan. Pluck the meat very finely, also scrape the meat from the bones.
Melt the butter in a large saucepan over low heat. Add the flour, stirring constantly with a wooden spoon. Slowly add the broth, stirring constantly, bring to the boil and simmer for a few minutes. Put all the meat in and let it get hot again.
Take the soup off the stove. Beat the egg yolks with lemon juice in a bowl and stir in 2 glasses of hot soup. Then add this to the soup and stir in well.
Season the soup to taste, pour into a terrine and stir well again. The soup should be creamy, if necessary add a little hot water to dilute the soup. Briefly melt the butter in a pan and stir in the paprika powder. Drizzle the pepper butter over the soup and serve the soup sprinkled with croutons.