What is a common garnish for French onion soup?

Gruyère cheese is a traditional and common garnish for French onion soup. When preparing this classic dish, the soup is typically topped with slices of toasted bread, which are then covered with Gruyère cheese before being placed under a broiler. This allows the cheese to melt and develop a golden brown, bubbly crust, enhancing both the flavor and the presentation of the soup. Gruyère's nutty flavor complements the caramelized onions in the soup, creating a rich and satisfying taste experience.

While other options may be delicious in different contexts, they are not standard for French onion soup. Parmesan cheese, crème fraîche, and chopped parsley can be used in various dishes, but they do not provide the distinctive taste and texture that Gruyère cheese brings to this iconic soup. The melted Gruyère is integral to the overall experience, making it the highlight of this culinary offering.