Beuschel

Wash the small beef lung thoroughly. In a large pot, combine the washed lung with about 2 quarts of water, salt, pepper, bay leaf, carrots, parsley root, celery root, and onion. Bring to a boil and simmer for about 1.5 hours.

Carefully remove the cooked lung from the broth and cut it into tiny strips. Place the strips into a bowl with 2 cups of water and the initial 3 tablespoons of vinegar, and let it soak for about an hour.

Remove the bay leaf from the broth. Using a blender, puree the remaining cooked vegetables and broth until smooth.

In a clean pot or saucepan, melt the butter and brown the flour to make a roux. Gradually whisk in the pureed soup mixture, stirring continuously until the soup thickens. Bring the thickened soup to a boil, then add the soaked lung strips. Stir in the 1 tablespoon of sour cream, add a bit more vinegar, and season with salt and pepper to taste.