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Published December 14, 2022. This post may contain affiliate links. Please read my disclosure policy.
This delicious classic French Onion Soup recipe with slowly caramelized onions is served with Crostini’s and Gruyere cheese. You will love the depth of flavors in this soup.
French Onion Soup
French onion soup is a simple-to-prepare soup consisting of slow-cooked onions that are then simmered in a rich broth and served in a bowl with crostini and melted cheese. There are a few variations, including the herbs used, wine, broth, and toppings. This is a very classical soup served throughout France during the winter months.
Different onion soups have been made since the Roman times and were often regarded as peasant food since onions were so easy to come by. It was made popular in the 19th century in Les Halles, the largest open-air market in Paris.
Ingredients and Substitutions
- Butter – I always use unsalted butter in my cooking and baking.
- Onions – I use yellow and white onions and garlic, but you can also use sweet onions.
- Wine – Cabernet sauvignon is a great deglazing wine for this. However, you can substitute with merlot or shiraz.
- Stock – I used to use a combination of beef stock and chicken stock, but now I exclusively use beef stock.
- Herbs – fresh thyme adds some great flavor to this onion soup.
- Vinegar – This may be controversial, but the vinegar will bring out amazing flavors in this soup. In addition, I also add sugar for a touch of sweetness.
- Crostini – These are placed on the soup before serving it. You can also use croutons.
- Cheese – Classically comté or gruyere are used.
How to Make French Onion Soup
Start by cutting the onions into thick slices.
In a large rondeau over medium-low heat, melt the butter and caramelize the onions very well while occasionally stirring, which can take up to an hour.
Halfway through the cooking process, you can add in some sugar to help brown and add more sweetness. This will be heavily scrutinized. Sugar makes caramel, so it’s the same thing in this soup. Sometimes you may find that your onions aren’t getting sweet, maybe because of the way that specific batch is, and you may need some sugar.
Once caramelized, add in the garlic and sweat for 3 to 4 minutes.
Next, de-glaze with red wine and cook the liquid until it is mostly absorbed into the onions. This process is known as “au sec.”
Next, add the beef stock and simmer for at least 20 minutes.
Finish with fresh thyme, salt, and pepper, and adjust with balsamic vinegar.
Pour the soup into an oven-safe bowl, top off with a few crostini, and add at least ½ cup to 1 cup of shredded gruyere cheese.
Place the soup on a sheet tray and cook it under the broiler for 3 to 4 minutes or until the cheese is browned and melted.
Make-Ahead and Storage
Make-Ahead: You can make this French onion soup up to 1 day ahead of time. Follow the reheating instructions below.
How to Store: You can store this covered in the refrigerator for 4 to 5 days. This will also freeze covered for up to 6 months. Thaw in the refrigerator before reheating and serving.
How to Reheat: Add the desired amount of onion soup to a medium-sized saucepot and cook over low heat until hot. Adjust the seasonings with salt and pepper and serve.
Chef Notes + Tips
- If you are finding that your onions are not browning, you can turn the heat up slightly while frequently stirring.
- We used to make a 5-onion soup at a different restaurant I worked at where we used white, yellow, red, leeks and garlic and then topped off with a bleu cheese crouton. In addition, we would add cream to this soup during the wintertime. Feel free to get creative.
- Feel free to add more cheese to the crostini before baking.
More Soup Recipes
- Clam Chowder
- Pork Confit and Split Pea Soup
- Broccoli Cheddar Soup
- Zuppa Toscana
- Chicken Dumpling Soup Recipe
Classic French Onion Soup Recipe
- 3 ounces unsalted butter
- 4 peeled and thickly sliced yellow onions
- 4 peeled and thickly sliced white onions
- 1 ½ tablespoons sugar
- 6 finely minced cloves of garlic
- 2 cups of red wine
- 12 cups beef stock
- 2 tablespoons chopped fresh thyme
- 2 tablespoons balsamic vinegar
- 16 crostinis
- 4 cups shredded gruyere cheese
- sea salt and fresh cracked pepper to taste
- Heat the butter over low heat in a large pot until melted.
- Add the onions and caramelize them very well while occasionally stirring, which can take up to an hour.
- Halfway through the cooking process, you can add in some sugar to help brown and add more sweetness. This will be heavily scrutinized. Sugar makes caramel, so it’s kind of the same thing in this soup. Sometimes you may find that your onions aren’t getting sweet maybe because of the way that specific batch is and you may need some sugar.
- Once caramelized, add in the garlic and sweat for 3 to 4 minutes.
- Next, de-glaze with red wine and cook the liquid until it is mostly absorbed into the onions. This process is known as “au sec.”
- Next, add the beef stock and simmer for at least 20 minutes.
- Finish with fresh thyme, salt, and pepper, and adjust with balsamic vinegar.
- Pour the soup into an oven-safe bowl and top off with a few crostini’s and add at least ½ cup to 1 cup of shredded gruyere cheese.
- Place the soup on a sheet tray and cook it under the broiler on high for 3 to 4 minutes or until the cheese is browned and melted.