French onion soup is two slow hours that cost about $3: 1.5 kg of thinly sliced onions caramelize for a full hour in olive oil and butter while a clear beef broth builds itself in a slow cooker — seared beef, browned vegetables, an onion with its skin on for color. White wine, soy and Worcestershire deglaze the jammy onions, the strained broth joins them, and each bowl gets fried baguette slices under a heavy mozzarella lid, grilled 5 minutes at 200 °C. The Paris market porters’ breakfast, restaurant price optional. Serves 4.
Instructions
- 1
Slice 1.5 kg of onions thin — thin gives up its sugar faster. Goggles help: block the gas before it reaches your eyes and there is nothing to cry about.
- 2
In your biggest pot, warm olive oil with 70 g of butter, add all the onions and let them steam in their own water at first.
- 3
Stir, and keep stirring, for a full hour over moderate heat — the color comes from sugar, and sugar needs time, not heat. Done means deep gold that spreads like jam.
60:00 - 4
Meanwhile, halve an onion with its skin on, rough-chop the carrot and celery, and brown them in a pan — raw vegetables make a thin broth, browned ones make a deep one.
- 5
Sear the beef hard in the same pan — that crust goes into the broth with it.
- 6
Load a slow cooker with the browned vegetables (skins on), peppercorns, thyme, bay leaves, the beef, the vinegar and 2 L of water. Lid down, one hour — a hard boil turns broth cloudy, gentle keeps it clear.
60:00 - 7
When the onions are jam-deep, deglaze with the white wine, then stir in the soy sauce and Worcestershire.
- 8
Strain the broth — everything in it has done its job — and combine it with the onions in one pot.
- 9
Add the salt, bring to a gentle simmer, drop in the last 50 g of butter and give it 5 more minutes.
05:00 - 10
Cut the baguette thick and fry the slices in olive oil — about 2 minutes, one flip, firm enough to hold what is coming.
- 11
Fill ovenproof bowls to the rim, float two bread slices on each, and cover completely with grated mozzarella — go heavy, any gap turns into a hole.
- 12
Grill at 200 °C / 400 °F until the cheese lid is molten and pulling.
05:00
Watch the video
Notes from our kitchen
The pale stage around the half-hour mark is where most people give up — push through it, the deep gold arrives all at once near the hour. If you are tempted to turn the flame up, don’t: high heat trades sweet for bitter. The skin-on onion is not laziness, it is what colors the broth. And when the cheese goes on, cover the bread completely and go heavier than looks reasonable — mozzarella shrinks as it melts, and any gap in the lid becomes a hole in the crust.
Variations
- Gruyère instead of mozzarella. Gruyère is the classic French choice — nuttier and more savory, with less of the dramatic pull. The video goes mozzarella precisely for that pull; split the difference with half of each if you want both the flavor and the cheese-strings.
- No slow cooker. Build the broth in a normal pot at the lowest flame with the lid on — the slow cooker is only there because nothing boils away in it. Watch that it never climbs past a gentle simmer; a hard boil is what turns broth cloudy.
Frequently Asked Questions
Why do the onions take a full hour?
Because caramel color comes from the onion sugars breaking down, and that chemistry runs on time, not temperature. Turning the flame up does not speed it up — it scorches the edges and turns sweet into bitter. An hour of stirring is the entire recipe; everything else is assembly.
Can I make it without the beef?
The beef is there for the broth, not the bowl — it is strained out. For a meatless version, brown the vegetables harder and lean on the soy and Worcestershire (or a vegetarian Worcestershire) for depth; the soup stays rich because the onions, not the meat, are the base flavor.
Why fry the bread before it goes on the soup?
Thin, soft bread drowns — it soaks through and sinks before the cheese sets. Thick slices fried firm in olive oil hold the mozzarella lid on top of the bowl, so you get the crust-then-soup layering that makes the dish.
Can I make it ahead?
The soup base — onions plus broth — is actually better the next day and holds in the fridge for several days; the flavors keep folding together. Assemble the bread-and-cheese top only when serving: reheat the base to a simmer, then bowl, bread, cheese, oven.
