For baked green bean soup, first peel and finely chop the onion. Peel the potatoes and cut into cubes. Wash and trim the green beans.
Melt butter in a pot and sauté the onion cubes in it. Stir in flour and let it brown a bit. Deglaze with vinegar and pour in the soup. Add green beans and potatoes and cook for about a quarter of an hour until soft. Then let it cool down a bit.
Stir the sour cream into the burnt green bean soup.