Is French Onion Soup Gluten-Free?

No, traditional French Onion Soup is not gluten-free. The soup often contains flour as a thickening agent, and the croutons that are added to the top are bread-based, putting them off-limits to those who can’t eat gluten. However, you can make a few substitutions like using gluten-free bread for the croutons and cornstarch instead of flour to make the soup gluten-free.