French Onion Soup

Cultural context

French onion soup builds its entire flavor from onions cooked low and slow until they turn deeply caramelized, a technique that transforms a humble, inexpensive vegetable into the base of a rich, savory broth. The dish is often tied to the market workers of Paris's old Les Halles district, who were said to eat it in the early morning hours, though onion soup itself has much older roots in French home cooking.

Listahan note

This version cooks the sliced onions low and slow for far longer than most home cooks expect, adding a touch of sugar partway through, since true caramelization — not just softened, translucent onions — is what gives the broth its depth, and rushing this step is the single most common reason the soup ends up thin-tasting.

Technique cues

• Cook the sliced onions over medium-low heat for 45 minutes to an hour, stirring occasionally, until they turn a deep amber-brown throughout rather than pale gold; shortcuts at this stage leave the broth tasting more like onion water than true French onion soup.
• Add a small pinch of sugar partway through cooking to help the onions along, and deglaze the pan with a splash of the broth or wine whenever fond builds up on the bottom, scraping it back into the onions rather than letting it burn.
• Simmer the caramelized onions in beef broth for a good stretch of time after they're done browning, letting the broth pick up their flavor fully rather than serving the soup the moment the onions and broth combine.
• Toast the baguette slices separately before floating them on the soup, since untoasted bread turns to mush almost immediately once it touches the hot broth.