Do You Have To Use Gruyère Cheese For French Onion Soup?

Of all the classic soup recipes out there, French onion soup just might be one of the most deliciously comforting. A hearty brew of sliced onions caramelized in butter, simmered in beef stock, and then topped with hearty croutons weighted down with plenty of melted cheese, French onion soup has been around since as early as the 14th century, when an early version of it appeared in Taillevent's cookbook "Viander," according to VICE. But the warming soup truly came into fashion in 1930s and '40s Paris, when various working-class restaurants surrounding the city's hulking Les Halles market decided to add the soup's pièce de résistance: that raft of a crouton gratinéed with a mountain of cheese (via VICE). With this hearty addition, French onion soup — or Gratinée des Halles, as it was known at the time — became both a popular breakfast among the market's many workers as well as an early morning hangover cure for partygoers exiting the city's cabarets.

Seeing as how French onion soup's cheese-capped bread is most likely what made this dish so enduring, it's an important part of the recipe to get right should you make it at home. When compiling your shopping list for the soup, you may have noticed that most recipes call for Gruyère as the cheese of choice to top the crouton. But is that the only acceptable cheese for this classic dish?

Yes, you must use Gruyère

The simple answer is yes. While you can substitute items in many recipes, when it comes to classic French onion soup, you simply must use Gruyère and no other cheese (via The Kitchn). While other cheeses such as Emmental, Comté, and fontina have similar properties to Gruyère, according to Food52, there's really no substitute for Gruyère's nuttiness, richness, and meltiness. While you could use another French or Swiss cheese to top your soup's crouton, it just wouldn't evoke French bistro food in the way that the OG Gruyère so easily does.

Now that you know exactly which cheese to select for that all-important crouton, you might be wondering just how to prepare that bready, cheesy raft. There are a few ways to do so, but we'll defer to French cooking expert Julia Child on this one. In her recipe, Child takes thick slices of French bread drizzled with olive oil and toasts them well in a 325-degree oven. Then, she floats the slices of toasted bread right on top of a big oven-safe casserole of soup (you can portion the soup into individual ramekins if you prefer), mounds them with plenty of grated cheese — right out to the bread's edges, to prevent any burning — tops the cheese with a bit of butter or oil, and runs the casserole right under the broiler, where the cheese melts, bubbles, and browns. As Child would say, "Bon appétit!"