French Onion Soup

Lunch | French

Prep time: 40 min Cook time: 2 min Servings: 6

French onion soup is one of the first dishes you get taught in chef school because it covers two foundational skills, caramelising onions and making a good stock. It also happens to be one of the most popular soups on steakhouse menus around the world. The whole dish is about coaxing as much flavour as possible out of a pile of cheap onions, then crowning the result with crunchy croutons and bubbling Gruyère cheese. On a cold night, there’s not much I’d rather eat.

Key Steps to a Great French Onion Soup

The Onions

The most important step in this recipe is caramelising the onions properly. The more colour you get on them, the better the soup will taste. Cut them with the grain rather than across, and keep the slices a consistent thickness so they cook evenly. You’ve got two ways to do this. Slow, over an hour and a half on low heat, stirring every 10-15 minutes. Or fast, around 25 minutes on a higher heat where you can’t really leave the pan. You want a deep, rich golden brown. If they tip towards black they’ll taste bitter, so keep a close eye on the colour.

Soup Base

Once the onions are caramelised, we'll add a splash of brandy. If you’ve got a gas burner it may catch fire as the alcohol vapour ignites. If this happens, just stand back and let it burn off. Then we'll add flour and cook it out similar to a roux. This is what gives the soup its slightly thickened, silky body. Then the beef stock, Worcestershire sauce and a small pinch of Maggi seasoning round out the umami. Throw in a whole sprig of rosemary, simmer for 20 minutes, and you’re done.

Crouton and Cheese

The ratio of crouton to soup matters, you want enough crouton to soak up the broth and still have texture left. Slice a French baguette about half a centimetre thick, drizzle with olive oil, season with salt and toast in the oven until dry and golden. To assemble, give the pot a stir so the onions don’t all sit at the bottom, then ladle into ovenproof bowls. Pile on the croutons, top with plenty of grated Gruyère and slide under the broiler until bubbling and golden.

Ingredient Notes

Beef stock: I think homemade beef stock is best, but i understand many won't have that in the fridge, so your butcher’s stock is the next best thing. If all you can get is supermarket stock, grab a bone broth instead, it’s usually richer and more gelatinous than the regular shelf-stable stuff.

Gruyère cheese: Gruyère is the classic for French onion soup. It melts beautifully, browns properly under the grill and has that nutty, slightly funky flavour that holds up against the rich broth. Comté or Emmental are good swaps if you can’t find it. Don’t substitute mozzarella, it doesn’t have the flavour and goes too stringy.

Maggi seasoning: Maggi is basically liquid MSG and it lifts the whole soup. You’ll find it in most supermarkets or any Asian grocer. A small pinch is plenty in a big pot. If you don’t have it, you can use straight MSG, or skip it. The soup will still be good, just slightly less rounded.

Equipment

Chopping board
Chef’s knife
Large heavy-based pot (Dutch oven works well)
Wooden spoon (flat-edged if possible)
Ladle
Grater
Ovenproof soup bowls
Baking tray
Tongs

Ingredients

2kg brown onions, thinly sliced
50ml olive oil + drizzle for croutons
100g (3.5oz) unsalted butter
salt
2 bay leaves
100ml brandy
2 tbsp flour
6 dashes Worcestershire sauce
4 dashes Maggi seasoning
1L (1 quart) beef stock
2 sprigs rosemary
1 baguette, thinly sliced
150g (5.3oz) Gruyère cheese, grated

Directions

To a large pot over medium-high heat, add the butter and oil. When the butter is melted, add the sliced onions with a big pinch of salt.
Stir well and turn the heat to medium-low. Cook the onions slowly for 1.5 hours, stirring every 5-10 minutes. (You can do this faster at a higher heat, but you will need to stir more frequently.)
Once the onions are caramelised and have a gooddark colour, add the bay leaves, then the brandy (if you’re using it gas stove, the brandy can catch alight) and allow the alcohol to burn off.
Preheat the oven to 180°C (350°F).
Next, add the flour to the onions and stir.
Add the Worcestershire sauce and Maggi seasoning, followed by the beef stock and rosemary. Stir and simmer for 20 minutes.
Add your sliced baguette to an oven tray, drizzle with olive oil and season with salt. Toast the sliced bread on both sides for 4-5 minutes each side.
Ladle the soup into your oven safe bowls, then add 2-3 croutons to the top, followed by the grated cheese.
Place under the grill of your oven until the cheese is golden brown and bubbly.

Recipe notes

Chef Tips

Cut the onions with the grain

Cut from root to tip, not across. With-the-grain slices hold their shape better and caramelise more evenly than across-the-grain ones, which tend to fall apart and turn to mush before they brown properly.

Scrape the bottom of the pot every time you stir

The caramelised sugar sticking to the bottom of the pan is called the fond, and that’s where most of the flavour comes from. Use a wooden spoon with a flat edge and push everything off the bottom as you stir. Just moving the top of the onions around does nothing.

Rescue dark onions with water

If the pan gets away from you and the onions are heading from deep brown to black, splash in half a cup of water. It cools the pan, lifts the caramelisation off the bottom and gives you a few extra minutes. Dark brown is what you want. Black tastes bitter and there’s no fixing it once you’re there.

Storage

The soup keeps in the fridge for 3 days and freezes for 2 months without the cheese and croutons on top. When you reheat, warm the soup back to a simmer, toast fresh croutons, then build and grill as for the original. The cheese needs to be done fresh, leftover French onion soup with stale cheese on top isn’t worth the effort.

FAQs

Can I use a different cheese? Comté and Emmental are both good swaps if you can’t find Gruyère, they have a similar nutty, melty character. Avoid mozzarella, it doesn’t have the flavour and goes too stringy. A mix of Gruyère and Parmesan also works beautifully if you want a sharper top.

Can I make this without the brandy? Yes. Cognac, dry sherry or a splash of dry white wine all work as a substitute. The point is to deglaze the pan and add some depth, not to taste the brandy itself. If you want to skip alcohol entirely, use a splash of beef stock to deglaze instead.

Can I caramelise the onions in advance? Yes, and it’s what I’d recommend for a dinner party. Cook the onions to deep golden brown, cool, then store in the fridge for up to 3 days. When you’re ready to serve, get them back in the pot, add the brandy and continue from there. Cuts the day-of cook time down to about 30 minutes.