Classic French Onion Soup

Classic French Onion Soup is a perfect union of sweet caramelized onions, crusty french bread croutons, and bubbly melted cheese. Our tried-and-true, easy-to-make recipe is rich, savory, and satisfying to the bone.

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Classic French Onion Soup is a perfect union of sweet caramelized onions, crusty french bread croutons, and bubbly melted cheese.

What kind of onions work best for French Onion Soup? 

The type of onions you use can dramatically impact  both the cooking time and the sweetness level of your soup. It may seem counterintuitive, but avoid using sweet onions for caramelizing.

When making anything with caramelized onions, I prefer to use a mixture of red and yellow onions. Sweet onions will work, but will take significantly longer to cook, and the end-product will have less flavor than that made with red and/or yellow onions.

You might be wondering what causes this sweetness inversion, so here’s the scoop: plain old red and yellow onions have a far more complex flavor profile than do sweet onions. While we perceive sweet onions to be sweeter, yellow and red onions have more pungent lachymators (i.e., stuff that makes you cry) than do sweet onions (e.g., WallaWallas, Vidalias, etc.), giving the impression that the red and yellow onions have a higher sugar content, when the opposite is actually true. It is because of their higher sugar content that red and yellow onions yield richer caramelized onions, and subsequently, more flavorful French Onion Soup.

Does it matter how the onions are cut for caramelizing? 

You wouldn’t think so, but apparently, it does. According to America’s Test Kitchen, slicing onions from pole to pole (root to stem) instead of cross-grain prevents them from breaking down too much during the long cooking process.

What’s the difference between “browning” and “caramelizing”?

Browning is the relatively quick process of browning the outside of onions, done in hot oil at relatively high temperature.

Caramelizing, on the other hand, is a much slower process; requiring no less than 45 minutes (and upwards from an hour for larger quantities) over much lower heat.

Caramelization describes the chemical reactions that take place when any sugar is heated to the point that its molecules begin to break apart and generate hundreds of new flavor, color, and aroma compounds. [Cook’s Illustrated]

This slow cook is necessary in order for the chemical process to occur that transforms the sugars in the onions into rich, jammy, umami goodness. This magical transformation only happens after a long cooking time. The more caramelized, the deeper will be the color of the onions and the more intense the flavor.

You can encourage the caramelization process by adding a teaspoon or two of sugar to the onions as they cook; however, the process cannot be rushed. Doing so may result in bitter onions; and subsequently, bitter soup.

Using the traditional stove-top method, caramelizing the onions for this French Onion Soup recipe will take at least 45 minutes, and up to an hour. (I make mine in the slow cooker, over a period of about 18 hours.)

Good news! You can freeze caramelized onions!

Did you know you can freeze caramelized onions? Make a big batch – the easy way (in a slow cooker!) – and freeze them. Then you can have this easy-to-make soup on the table in just 30 minutes, anytime you want!

What kind of cheese is best for French Onion Soup? 

Traditionally, French Onion Soup is topped with a bubbly, broiled Gruyère cheese. Gruyère is a Swiss-type or Alpine cheese.

Gruyère has a distinctive but not overpowering taste and gets excellent scores for meltability. The flavor of Gruyère can vary wildly, depending on both cheesemaker and age. Like Jarlsberg, young Gruyère is described as creamy and nutty, with the later becoming more earthier as it matures. Fully aged Gruyère can have a slightly grainy texture, like that of aged cheddar.

Depending where you live, it can be difficult to find good Gruyère. If you have this problem, do not – for the love of all Kitchen Elves everywhere – do not buy anything with the words “processed” in its name to melt on top of your hard-earned caramelized onions (unless you enjoy eating melted Play-doh). Instead, go with one of these delicious alternatives.

Gruyère Cheese Substitutes

Fontina and Parmesan: In the absence of Gruyere, the Fontina & Parmesan combo is my personal favorite cheese finish for French Onion Soup. (The soups shown throughout this post are all topped with this mixture.) 

Fontina is a semisoft, very meltable cheese with a slightly nutty, savory flavor. Fontinas from the United States usually have a milder flavor and softer texture than do those from Europe. (I don’t think I’d use a European Fontina for this soup.)

Jarlsberg: Jarlsberg is my favorite everyday cheese. It’s smooth, sweet, nutty flavor complements French Onion Soup and pulls the sweet notes from the soup. Really good choice. (The only reason I list Fontina first is because, objectively, as far as flavor and meltability are concerned, it is more closely aligned with Gruyère.)

In a pinch, any mild, meltable Swiss cheese will work. Just choose a cheese you love, grate it up, and enjoy!

Should I use a Baguette or a Batard? (And what the heck is a Batard, anyway?)

French baguettes are the usual crouton of choice for French Onion Soup; however, I prefer to use French Batard.

A batard is the lesser known cousin of the thin, sexy French baguette. Usually about a foot or less long, the batard is much thicker around than the baguette, with a slightly thinner crust. I find that batard croutons make for a better soup-eating experience: they are easier to spoon up, and not quite as chewy as those made from baguette rounds. 

No fancy french breads? No worries! Everyday grocery-store French bread will also work just fine. Your choice of bread for the croutons is totally up to you. 

A Note about Soup Stock

A soup is only as good as the stock upon which it is built. 

French Onion soup is traditionally made with beef stock (or broth); however, you can make it with chicken or vegetable stock if desired. 

If you make your own soup stock, use a light version. You don’t want the flavor of your stock to overwhelm the subtleties of the caramelized onions. You should be able to see sunlight through a jar of your stock. If it is too thick to see the light, add a little water, or a 75/25 combination of water and wine.

Always taste any stock, including boxed stocks, before you use them. A bad stock can ruin an entire soup; a great one can elevate it.  If you don’t like the flavor of your stock, don’t use it. 

No need to worry about fancy soup crocks if you don’t have them: you can serve French Onion Soup in any individual, oven-safe vessel. Garnish with a sprig of fresh thyme and you’re all set! 

Recipe Updated February 9, 2021 (Originally published November 21, 2013)

How to Lighten Up Classic French Onion Soup

If you prefer the classic, intensely flavored French Onion Soup, use beef broth and red wine as listed first in the recipe.

Mr B and I, however, prefer our French Onion Soup on the lighter side of traditional, both in sodium load and flavor profile. For this reason, we often sub in a light chicken stock or vegetable stock (for a vegetarian French Onion Soup) in place of the traditional beef broth base, and white wine instead of the customary red or port. 

Either way, it’s delicious! 

Note that if you sub in a vegetable stock, take care that it doesn’t have a strong flavor, as it will affect the outcome of your soup.

Homemade soups are some of our favorite things. Be sure to check out these delicious, time-tested  classic soup recipes, including Loaded Baked Potato, Hungarian Mushroom, and the easiest Ham-bone Split Pea Soup you’ll ever make! 

I’m not big on excessive kitchen gadgets, but this herb stem stripper is a thumbnail saver – and totally worth the real estate it takes up in my kitchen drawer. To use it, you just thread the stem through the smallest hole through which it will fit, and pull the stem through. Like magic, the herb leaves fall away, ready to use. It works like a charm on fresh thyme! 

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