Which type of cheese is used in the French onion soup?

In French onion soup, Gruyère cheese is traditionally used for its unique flavor and melting properties. Gruyère, a Swiss cheese, has a distinct nutty and slightly sweet taste that enhances the rich, caramelized onion broth. When broiled on top of the soup, it melts beautifully and creates a deliciously gooey layer that complements the dish's texture and flavor.

While other cheeses might be used in variations, such as Swiss or even cheddar, Gruyère is recognized as the classic choice that aligns with authentic French culinary practices. This cheese not only adds to the overall depth of flavor but also provides that appealing golden crust when baked, making it an essential component of the dish.