Prepare a clear soup.
Peel the onions and cut about 10% into very fine cubes. Quarter the rest of the onions and cut them into relatively fine slices (1 to 2 mm thin).
Heat the oil in a high saucepan and sauté the 10% finely diced onions until golden.
Sprinkle with the flour and fry until the first onion pieces become very dark and add about a quarter of the clear soup.
Add the rest of the onions and slowly pour in the rest of the soup. Cook under moderate heat until the onions are soft but still have some “bite”.
Season with pepper if desired and serve.