For the spicy-sour soup, prepare a beef broth and bring to a boil. Grate the crust from the rolls and soak in the milk.
Add the rolls to the soup together with the sour cream and a little butter and puree everything. Season to taste with salt and pepper.
Chop the chives and dice the brown bread. Roast the cubes together with half of the chives in a pan.
Serve the spicy-sour soup sprinkled with black bread croutons and the rest of the chives.