Soupe à l'Oignon

Soupe à l'oignon is onions cooked down for an hour, simmered in broth, and gratinated under bread and melted cheese. It is a dish made almost entirely of patience — everything good about it happens in the first step.

What it actually is

Thinly sliced onions are cooked slowly in butter for anywhere from thirty minutes to an hour. They collapse, lose their water and turn deep brown and genuinely sweet. This cannot be hurried: onions rushed over high heat go bitter instead of sweet, and no amount of broth will hide it.

The pan is deglazed with white wine or a dry sherry, then simmered with beef broth, thyme and bay.

To serve it gratinée — the version most people mean — the soup goes into an oven-proof bowl, gets a slice of stale baguette and a thick layer of grated Gruyère or Comté, and goes under a hot grill until the cheese browns and runs over the rim.

It belongs to Paris, and specifically to the old Les Halles market, where it was eaten late at night and at dawn by market workers coming off a shift.

How it's served

• Gratinated, in the bowl it was grilled in — arriving dangerously hot.
• Ungratinated as a plain soup, with the bread and cheese on the side.
• As a late dish, which is its historic role.

Writing it on a menu

• Say whether the broth is beef. This is the detail that decides whether a vegetarian can order it, and the soup reads vegetarian to most people.
• Say whether it comes gratinated; guests picture the cheese crust and are disappointed by a plain bowl.
• Note the allergens: gluten in the bread, dairy in the cheese, alcohol from the wine.
• Warn that the bowl is very hot — worth a line, and it saves a burnt hand.