Preparation time: 5 minutes
Cooking time:  Less than 30 minutes
 

This is the version of onion soup that is best-known throughout the world.

The Larousse Gastronomique says that while onion soup is a tradition of Lyon, the version gratinéed with cheese, traditionally served in Les Halles and Montmartre, is Parisian. There is more bread and more cheese and the broth is much less rich.  

1. Slice the onions thinly.
2. In a large pot, heat the butter until foamy, or heat the butter-oil mixture.
3. Sweat the onions over low heat for 15 minutes or until translucent and lightly browned.
4. Add the flour and mix well.
5. Stir in the broth; bring to a boil, then simmer another 15 minutes. Season to taste.
6. Place four oven-proof bowls on a baking sheet (easier to handle). Ladle in the onion soup. Top each one with a slice of country bread and sprinkle generously with the cheese.
7. Place under the broiler until the cheese is bubbly and browned.
8. Remove and serve.