Heat the butter in a saucepan, sweat the flour in it, then pour in the finely chopped onion and cook until translucent. Pour in the clear soup, stir well, let it bubble and cook heartily for 8 min. Stir the yeast with a little water until smooth, add to the soup and cook for another 5 minutes. Cut bread into cubes, toast in a frying pan in a little butter until light brown. Serve the soup sprinkled with bread cubes.
Cuisine of the countries of Europe. Heyne, 1984