Toast flour in frying pan over good heat, stirring, until hazelnut brown, cool slightly. Add butter or light butter, mix with flour. Add onion, steam for a few minutes. Add soup, bring to a boil while stirring, simmer on low heat for 20 min, stirring occasionally. Grate cheese.
Serve: Divide soup evenly into warmed plates, sprinkle cheese as desired or serve separately with it at table.
Prepare: Cook soup the day before, cool. Cover and keep in refrigerator. Reheat carefully.
Tips: Flour can be toasted in advance. Add a little strong red wine to the soup at the end. Sprinkle the soup with roasted onion rings, omitting the steamed onion strips.
Our tip: Use your favorite red wine for cooking!