French onion soup is a classic French soup made with onions, broth, bread, and cheese. It originated in France and has been popular for centuries, with many variations developed over time. The base of the soup is a flavorful onion broth, which gives the soup its distinctive sweet and savory taste.
Onion Broth
The key component that makes French onion soup special is the onion broth. This is made by slowly caramelizing onions in butter or oil over low heat for a long period of time, generally 45 minutes to 1 hour. This long cooking time breaks down the onions and concentrates their flavor, resulting in a rich, sweet, and intensely oniony broth.
Typically, the onions are sliced thinly so they cook down fully. Yellow, white, or red onions can all be used. Shallots are also commonly used in addition to onions, as they add even more onion punch.
Some recipes also include other aromatics like garlic, herbs, and wine in the onion cooking process to build even more flavor. But onions remain the star of the show.
Onion Varieties
The most common types of onions used for French onion soup are:
- Yellow onions – The most popular choice, they have a balanced onion flavor.
- White onions – Very mild in flavor but turn sweeter when caramelized.
- Red onions – These have a sharper bite and turn mellower when cooked.
- Shallots – More subtle and sweet than regular onions.
Yellow and white onions are ideal for achieving a rich, mellow, sweet depth of flavor. Red onions can be added for a bit more bite. And shallots make a great accompaniment for even more layered onioniness.
Broth Base
In addition to loads of onions, French onion soup is classically based on a meat or chicken broth. This provides deeper savory flavors and richness.
Beef broth is the most traditional choice, made with bones and meat. Chicken broth is lighter but still works well. Vegetable broth alone would make the soup one-dimensional, but it can be used in combination with meat broths.
Other ingredients like garlic, herbs, white wine, sherry, or brandy are also commonly cooked right in with the onions to build even more complex flavor in the broth.
Broth Options
Some common broth choices for French onion soup include:
- Beef broth
- Chicken broth
- A mix of beef and chicken broth
- Vegetable broth combined with meat broth
Cooking the Onion Broth
To make a flavorful onion broth, it’s important to cook the onions slowly and thoroughly.
First, slice the onions about 1/4 inch thick. Thinner slices will cook down faster. Use a combination of onion types if desired.
Then, melt several tablespoons of butter in a heavy bottomed pot over medium heat. Add the onions and cook for 15-20 minutes until soft and translucent, stirring occasionally.
Next, lower the heat to medium low and continue cooking the onions, stirring frequently. They will slowly caramelize and turn a rich brown color. This long cooking time of 45-60 minutes is essential for full caramelization and intense flavor development.
Optionally, garlic can be added about halfway through cooking. Other herbs, wine, or stock ingredients are also sometimes cooked right in with the onions.
Once the onions are a deep brown color and incredibly soft and sweet, the broth can be added. Use beef, chicken stock, or a mix. Simmer the broth for 30-60 minutes to meld the flavors.
The end result is a pot of delicious, rich and complex onion broth that serves as the base of an incredible French onion soup.
Toasts and Cheese
To finish French onion soup au gratin style, slices of bread topped with cheese are toasted or broiled on top.
Bread – Traditionally French bread is used, such as a baguette. The bread should be sliced about 1 inch thick to form croutons.
Cheese – Gruyere is the classic melted cheese topping, but Swiss, mozzarella, or provolone also work.
To assemble – Ladle the soup into oven-safe bowls. Float a slice of bread on top of each. Sprinkle cheese over the bread slices, completely covering them. Place under the broiler for a few minutes until the cheese bubbles and browns.
The toasted bread and melted cheese form the perfect crunchy, gooey, savory topping to contrast with the rich onion broth.
Complete French Onion Soup Recipe
Here is a complete recipe to make authentic French onion soup from scratch:
Ingredients
- 3 lbs yellow onions, sliced thin
- 2 tbsp butter
- 3 tbsp olive oil
- 1/4 cup dry white wine or sherry (optional)
- 6 cups beef broth
- 2 cups chicken broth
- Sprigs fresh thyme
- Bay leaf
- Salt and pepper
- Slices of French bread, 1 inch thick
- 1/2 lb grated Gruyere cheese
Instructions
- Heat butter and olive oil in a large pot over medium heat. Add sliced onions and cook for about 20 minutes until soft and translucent, stirring occasionally.
- Reduce heat to medium low and continue cooking onions for 45-60 minutes. Stir frequently and scrape the bottom to prevent burning. Onions will caramelize to a deep brown.
- Add wine or sherry (optional) and cook 2 minutes more to reduce.
- Add beef broth, chicken broth, thyme, and bay leaf. Season with salt and pepper. Simmer soup for 30 minutes.
- Preheat broiler. Place oven-safe bowls on a baking sheet. Ladle soup into bowls. Top with bread slices and cover with grated Gruyere.
- Broil bowls for 3-5 minutes until cheese is completely melted and bubbly.
- Remove bowls from oven and allow to cool for 2-3 minutes before serving.
Tips for Making the Best Onion Broth
Here are some top tips for achieving maximum flavor in the onion broth:
- Cook onions very slowly over medium low heat to achieve full caramelization.
- Frequently deglaze the pan by adding small amounts of stock or water to release browned bits from the bottom.
- Add a bit of sugar while cooking to enhance caramelization.
- Use a combination of onion types for complexity of flavor.
- Allow the broth to simmer for at least 30 minutes after adding stock to meld flavors.
- Skim excess fat from the top of the broth for cleaner flavor.
- Add aromatics like garlic, herbs, white wine, or sherry while onions cook.
Onion Soup Origins and History
Onion soup has long been a staple food in European cuisine. The concept of an onion-based soup dates back to Ancient Rome, where they were known as “imperial soup”.
Over the centuries, onion soups spread across Europe while incorporating regional influences. In France, it evolved into the modern classic French onion soup.
Some key moments in the history of French onion soup include:
- Middle Ages – Onion soups served across France and England, flavored with herbs.
- 1700s – Onion soups popularized in Paris, often served with croutons floating on top.
- 18th century – Gruyere cheese added as a topping after the cheese’s creation in Switzerland.
- 19th century – French onion soup became a fixture on Parisian bistro menus.
- 1910s – Recipe for Gratin??ed Onion Soup published by Louis Diat, cementing the modern version.
So while French onion soup has evolved over many hundreds of years, it remains a beloved staple today in both home and restaurant cooking.
Regional Variations
French onion soup is popular across France with regional twists on the classic preparation:
- Paris – Often finished with a touch of Cognac and Comt?? cheese.
- Lyon – Made with red wine instead of white and baked under a pastry crust.
- Alsace – Topped with bacon and Munster cheese.
- Nice – Enriched with tomato paste and Parmesan cheese.
While ingredients and toppings may vary, the underlying onion broth remains at the core of all French onion soup recipes.
Common Questions
Can I make it ahead of time?
Yes, the soup broth can be made 1-2 days in advance then reheated before serving. Do not add the bread and cheese until right before serving.
Can I freeze French onion soup?
The broth freezes well for up to 3 months. Thaw in the refrigerator before reheating and topping with bread and cheese.
Is sweet onion better?
No, regular yellow, white, or red onions are best to achieve a balanced, richly caramelized flavor.
Should I use low heat?
Yes, low gentle heat is essential during the long onion cooking phase. High heat will burn the onions rather than caramelize them.
What type of pot should I use?
Use a heavy-bottomed pot like enameled cast iron or stainless steel to cook the onions evenly without burning.
Conclusion
In conclusion, French onion soup achieves its incredible depth of flavor thanks to slowly caramelized onions. Thinly sliced yellow, white, or red onions are cooked over low heat in butter and olive oil for up to an hour. This long cooking time breaks down the onions and develops a sweet, rich, concentrated flavor.
The onion base is then simmered with beef and/or chicken broth, creating an umami-packed onion broth. To finish, the soup is ladled into oven-safe bowls, topped with toasted bread and melted cheese, and broiled to perfection.
French onion soup originated from ancient Roman onion soups, developing over centuries into the beloved French classic we still enjoy today. With its complex yet balanced flavors and indulgent melted cheese topping, French onion soup remains an iconic French specialty.