Recipe: French Onion Soup Casserole (2024)

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Tami Weiser

Tami Weiser

Tami is a writer, recipe developer, culinary educator, and caterer. She is a graduate of the Professional Culinary Arts program at the Institute for Culinary Education (ICE) in New York.

updated Feb 3, 2020

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Recipe: French Onion Soup Casserole (1)

This French onion soup casserole takes everything your know about the homey dish and gives it a rich and luxurious update. Expect big flavor on this one!

Serves8

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Recipe: French Onion Soup Casserole (2)

If you’ve got leftover caramelized onions, or you are about to make a recipe that uses them, double up. And while you’re at it, grab that loaf of leftover bread because you are about to embark on a trip to France in one delicious vegetarian casserole based on the famous soupe à l’oignon gratinée.

Caramelized Onions Are a Leftover Rockstar

Caramelized onions are a result of that magical mixture of onions and time, cooked slow and on a low heat, so the onion’s natural sugars come forward and the onions become jammy. This recipe includes making caramelized onions for the base of the casserole, but I do my best to have some on hand almost all the time. Caramelized onions also keep, refrigerated, for about three days in a covered container, and can even be frozen.

A Mini Guide to Caramelized Onions

  • How To Caramelize Onions
  • Why You Should Freeze Caramelized Onions (and 3 Ways to Do It)
  • 5 Mistakes to Avoid When Making Caramelized Onions

Stock: The Foundation Flavor in a Vegetarian Casserole

To stock or not to stock? That is the question raised by so many chefs and cooks when it comes to French onion soup’s base. Most onion soups are made with a beef stock, made from browned bones and plenty of vegetables and cooked ad infinitum. This recipe creates its own vegetable stock as you cook the ingredients. It takes less than half an hour and works as a wonderful, supportive base for the incredible caramelized onions. If you start the onions from scratch, assume it’s about an hour of cooking time.

The Joys of Day-Old Bread

Second-day bread is a kitchen wonder. This recipe puts that loaf of bread to full use — creating a mini-grilled cheese sandwich — all right on top of the casserole to soak into the deliciousness below.

Comments

This French onion soup casserole takes everything your know about the homey dish and gives it a rich and luxurious update. Expect big flavor on this one!

Serves 8

Nutritional Info

Ingredients

For the stew:

  • 8 tablespoons

    (1 stick) unsalted butter, divided

  • 7

    large yellow onions (5 to 5 1/2 pounds total), halved and cut into 1/4-inch-thick slices

  • 4

    large shallots (about 8 ounces), peeled and cut into small dice

  • 4 teaspoons

    kosher salt, divided

  • 1 teaspoon

    freshly ground black pepper, divided

  • 6 cloves

    garlic, minced

  • 5 stalks

    celery (about 12 ounces), including leaves, cut into small dice

  • 5 carrots

    (about 8 ounces), peeled and cut into small dice

  • 6 cups

    cremini and/or button mushrooms (about 1 1/2 pounds), sliced thinly

  • Cooking spray

  • 1/4 cup

    all-purpose flour

  • 1 cup

    dry Riesling wine

  • 6 to 8

    fresh sage leaves, minced, or 2 teaspoons dried sage

  • Leaves of 5 sprigs fresh thyme, finely chopped

  • 1

    (15-ounce) can white beans and their liquid (optional)

For the topping:

  • 1

    large baguette (about 1 pound), cut crosswise into 24 slices

  • 12 ounces

    Gruyere, Comté, or Raclette cheese, shredded

  • 4 tablespoons

    unsalted butter

Instructions

Make the stew:

  1. Heat 4 tablespoons of the butter in a large, heavy-bottomed pot or Dutch oven over medium-high heat until melted and just beginning to foam.

  2. Add the onions, shallots, 1 teaspoon of the salt, and 1 teaspoon of the pepper. Cook, stirring occasionally, until the onions are translucent and begin to brown on the edges, 5 to 7 minutes. Reduce the heat to low (or the lowest your stovetop will go) and cook, stirring occasionally and adjusting the heat as needed, until the onions are completely softened and caramel brown in color, about 30 minutes.

  3. Add the garlic, celery, carrots, and mushrooms (add the mushrooms in batches if they do not all not fit into your pot at once, as they will cook down and reduce in volume), and stir to combine. Once you have added all the mushrooms, cover and cook 20 minutes more.

  4. Arrange a rack in the middle of the oven and heat to 375°F. Coat a 9x13-inch baking dish with cooking spray and set aside.

  5. When the vegetables are ready, transfer them with a slotted spoon to a large bowl and set aside. Pour the remaining vegetable cooking liquid into another bowl or a measuring cup with a spout; set aside.

  6. Return the pot to high heat, add the remaining 4 tablespoons of butter, and cook until it is melted and begins to foam. Add the flour, whisk to combine, and cook until it is golden-blonde in color, about 2 minutes. Add the wine and whisk to combine.

  7. Add the reserved vegetable cooking liquid and whisk to combine. Add the sage, thyme, and remaining 3 teaspoons salt and whisk to combine. Add the reserved cooked vegetables and beans and their liquid, if using, and stir to combine. Pour the mixture into the casserole dish and spread into an even layer; set aside.

Make the crouton topping:

  1. Arrange 12 of the bread slices on top of the casserole in a single layer, pushing them down gently into the liquid and vegetables. Sprinkle with about half of the cheese. Arrange the remaining 12 slices of bread over the cheese in a single layer, then sprinkle the remaining cheese on top. Melt the butter in the microwave, then drizzle over the casserole.

  2. Bake until the cheese is melted and the casserole is bubbly, 20 to 22 minutes. Serve immediately.

Recipe Notes

Make ahead: This recipe can be broken into parts and cooked over several days: Make the onions one day, cook it with the vegetables the next, and make the sauce and put the casserole together on the final day. Reheat the vegetable mixture before finishing the casserole.

Slow-cooker vegetable preparation: You can also make this recipe a second way, as a make-ahead, if you are short on time. Prepare the onions as written, but then transfer them and all the vegetables to a slow cooker, stir, and set at low or medium-low and cook for 3 to 4 hours. Then scoop the vegetables out, make the roux (flour and butter mixture) on the stove, add the wine and vegetable cooking juices to the pan to make the sauce, and add the cooked vegetables as written.

Storage: This dish is best eaten fresh, as the bread absorbs liquid as it sits and the casserole will get soggy. If you have any leftovers, they can be stored in an airtight container in the refrigerator for up to 3 days.

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autumn

Baking

beans

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Canned Goods

Casserole

Recipe: French Onion Soup Casserole (2024)

FAQs

How to deepen the flavor of French onion soup? ›

A few sprigs of thyme and a bay leaf elevate the soup even more, but I take it a step further, adding a splash of fish sauce for complexity and depth—don't worry, it won't taste fishy—and a hit of cider vinegar to balance some of that oniony sweetness.

Why do you put baking soda in French onion soup? ›

The caramelized onions for this soup cook more quickly due to a pinch of baking soda but still have that deep, slow-cooked flavor. Topping the soup with hot, cheesy toasts prepared while the soup simmers, eliminates the need to bake the soup in specialty French onion soup bowls.

How do you make French onion soup less bland? ›

Most likely it could be from not caramelizing the onions long enough, as this is crucial for flavor development. Also, be sure to use a good quality broth and season the soup properly with salt and pepper. You can try adding a splash of balsamic vinegar or Worcestershire sauce for a boost of flavor.

What is the best wine for French onion soup? ›

I recommend a dry white or red wine, such as a good quality Pinot Grigio/Gris, Sauv Blanc, Sémillon, Chardonnay, Merlot or Pinot Noir.

How to thicken up French onion soup? ›

The easiest way to thicken your French onion soup is with flour. You can also use cornstarch if you don't have any flour. Remember to never add the flour or cornstarch directly to the soup – otherwise you run the risk of it clumping.

What is the etiquette for eating French onion soup? ›

I fear it's gauche to use a knife, but how am I supposed to cope with the thick layer of cheese on top? With such a soup, a knife is your friend, not your enemy. Using both the soup spoon and the knife, push the baked cheese against the rim of the cup or bowl and cut it gently with the knife.

Why is my French onion soup so bland? ›

If you don't add enough salt, pepper, or other herbs and spices, the soup may taste bland.

How to doctor up canned French onion soup? ›

Some fresh rosemary or thyme brings a woody, peppery taste to the soup, complementing the umami flavor of the beef stock. With a splash of balsamic vinegar and green onions or fresh basil as a garnish, the canned soup is transformed from a grocery store original into a gourmet dish.

How can I deepen my soup flavor? ›

"If your broth is lacking in savory richness, try adding roasted onion, tomato paste, mushrooms, seaweed, soy sauce, or miso. These ingredients add umami flavor and depth to broth," she says. The choice of ingredient depends on the recipe, though.

What is the best way to cut onions for French onion soup? ›

Get the oven to 400 degrees while you prepare the onions: Cut down through the poles of each onion, down through the root end into and through the stem end. Peel each half, keeping the flesh tethered at the root end. Slice 1/4-inch thick longways, pole-to-pole, using a mandolin if you have one.

Does French onion soup taste better the next day? ›

French onion soup often tastes even better when made ahead. You can prepare it up to two days in advance, refrigerate it, and then reheat it gently on the stovetop or in the microwave.

What bowls are best for French onion soup? ›

French onion soup is traditionally served in lionhead bowls, which are deep but not very wide porcelain bowls. Here are four reasons why these bowls are perfect: Plenty of soup. Even as the bread on top starts to soak up some of the soup, there's still plenty left underneath.

Can I use chicken broth instead of beef broth in French onion soup? ›

It is better to use chicken or vegetable broth rather than sub-standard beef broth. Best to use low salt and add salt if required. 4. Bread - The idea with the recipe is that you can use a spoon to cut through the bread into the soup to eat it (see video).

What is the difference between onion soup and French onion soup? ›

What is the Difference Between Onion Soup and French Onion Soup? French onion soup is always made with beef stock. Other onion soups can be made with chicken, vegetable, or beef stock. Additionally, French onion soup typically contains wine or sherry, which isn't typical or necessary in other onion soups.

Why add flour to French onion soup? ›

Flour: a little all-purpose flour will help to thicken the soup. You can feel free to use gluten-free flour. Dry white wine: this helps to deglaze the pan and add a boost of flavor.

What can you substitute for white wine in French onion soup? ›

If you prefer not to use Wine, you can substitute 3 Tablespoons white wine vinegar + chicken or beef broth to make 3/4 cup.

Why does my French onion soup taste bitter? ›

On the other hand, you can not caramelize onions for too long – they will be bitter. Salting the onions at the beginning of cooking helps to soften them more quickly. Photo 2 – this is how the onions will look like after 15 minutes of cooking time. Photo 3 – this is how they look like after 30 minutes.

What is impolite to do in France when eating? ›

Eating with your hands is considered impolite, so make sure to tuck into that steak frites with your knife and fork. Notable exceptions include bread and certain dishes including asparagus. One thing you may have noticed in France is people do not cut their salads. Do so, and you might receive a few funny looks.

Do people in France eat French onion soup? ›

The food writer Waverley Root comments that the origins of French onion soup may lie in Alsace, although the dish is popular throughout France and "apparently no region lays particular claim to it". Onion soups from other regions include the tourain from Quercy-Périgord and the ouliat from the Béarn.

Is French onion soup good for your gut? ›

Onions are a great source of soluble fibre and therefore a good prebiotic; food for the good gut bacteria. Optimal gut health is crucial for weight loss and this delicious soup provides great nutrients to help boost weight loss as part of a weight management programme.

How do you add depth of flavor to soup? ›

"If your broth is lacking in savory richness, try adding roasted onion, tomato paste, mushrooms, seaweed, soy sauce, or miso. These ingredients add umami flavor and depth to broth," she says.

How do I make my French onion soup darker? ›

The caramelized onions are what give the soup its rich dark flavor and color, so don't skimp! Use a good quality beef broth. We use Better Than Bouillon to make our beef broth because it's extremely flavorful and contains a decent amount of salt, which seasons the soup well.

What can I add to French onion soup that is too sweet? ›

The sweetness can be balanced by adding some dry wine or vinegar. Taste as you go and don't overdo it. A little salt will balance it too, but don't forget that the grated cheese you will top it with is salty.

References

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