Skills you will learn in this recipe
Slow-cooking onions; safely gratinating a classic French onion soup
Links to the last recipe
Making a dish featuring bread & cheese; flavouring with parsley; showcasing a star ingredient
This simple and delicious French onion soup was a real Saturday evening treat when Emily was growing up. There was something about the sweetness of the slow-cooked onions, matched with the savoury stock, nutty cheese and slightly chewy bread that made it incredibly moreish & satisfying. In the 1970s it also seemed quite bohemian!
Now it’s a French menu staple, but we suspect not that often cooked at home. But it’s very easy to make. And lovely to eat, so we strongly recommend you give it a try.
Bibi had an old-fashioned, and very fierce, gas grill that she’d use to melt the cheese on the croutons. It would make the soup bowls incredibly hot, and you had to mind your fingers! You also had to mind your mouth on the nuclear-hot cheese. Our oven grill isn’t quite up to that standard, and also we find oven-baking a safer method. But we also quite like the cheese a little less gratinated – the hot soup continues melting it as you eat.
The onions are the star here, and it’s worth looking for really large sweet ones. Roscoff onions are the holy grail of French onion soup, but they are expensive and hard to find, at least in the UK. So we look for either large Spanish onions, or mild white ones (or a mixture, as we used today). But regular large brown supermarket onions will work fine. And you need a lot of onions for French onion soup! You’ll be surprised by how many, as they will reduce down a lot. Today, for a soup that made four generous, but not ridiculous, portions, we used two extremely large brown onions, and four medium white ones.
The other flavourings in the soup are a question of some debate. Bibi kept hers simple with just a good beef stock, some mustard and a little thyme & parsley, letting the onions shine. We tend to agree. But many recipes add garlic (we think a thug in this recipe), balsamic vinegar (ditto), calvados or brandy, or many other flavours besides. We stick to Bibi’s formula, just adding a little cider vinegar for extra acidity.
The mustard Bibi used is worth a mention too. In the 1970s it was called, undoubtedly erroneously, ‘French mustard’ and widely stocked. It’s a very mild, sweet brown mustard, and now a bit hard to find. But it does give Bibi’s version of this dish a lovely and very distinctive flavour that it’s hard to replicate without it, so do shop around to find it. If you can’t get it, either a mild American-style mustard or a wholegrain mustard is probably the closest match.
We use beef stock, as Bibi did and as is traditional. But you can use chicken stock instead, or make the dish vegetarian with a vegetable stock. We top the French baguette croutons with a mixture of Gruyère, which again is traditional and melts well, and cheddar, as Bibi did, for an extra tangy-cheese hit.
French onion soup is easy to make, but you’ll need to plan ahead for it. First, the onions will benefit from a long, slow initial cook so they sweeten and caramelize slightly. At least half an hour, and ideally more like 45 minutes or more. But also the soup itself then needs to cook for at least an hour or more, but at that point you can largely just leave it unattended. It can also be made well ahead, and then kept until you are ready to add the croutons and serve.
You’ll see many French onion soup recipes that wax lyrical about caramelizing the onions. Most advocate a really long, slow cook, until the onions become very brown – many quote 90 minutes to 3 hours (and one 5 hours!). And frying onions need to be frequently stirred. Now, so many great chefs must have a point here, but we’re conscious that this is a cookery course, and primarily aimed at beginners. And who wants to (or has time to) spend three hours stirring onions? We also genuinely think the soup is delicious with about 30 to 45 minutes of frying the onions, so that is what we do.
Preparation & frying the onions
The main task in this whole dish is slicing the onions. But the good news is that large, mild onions are less likely to irritate your eyes. Peel the onions, then slice them quite thinly. See our onion Tip. You can chop the onions instead if you wish, but we prefer the texture of the soup with the onions sliced. When slicing, as you get just past the middle of the halved onion, a nice tip is to flip the rest on its side, as in the fifth picture below. This makes the remainder easier to slice.
It’s now a good idea to separate out the slices as much as possible. You could do this with your spoon or spatula when you start frying, but, with this volume of onions, this will be trickier. So spending a few minutes separating the slices now will make things easier later. We put the onions in a bowl, to make them easier to transport and add to the pan
To fry the onions, place a generous knob or two of butter along with some olive oil into the base of a saucepan or casserole large enough to hold the onions & finished soup. We’ll talk more about equipment later, but we use an oven-&-hob-proof large casserole, as we intend to finish the soup in a hot oven later. Set the pan over a medium heat until the butter melts.
Jake sticks his nose in
Remember Bibi’s tip. Butter adds flavour, but the oil prevents it from burning.
When the butter has melted, add the onions and stir well to coat them. Add a little more oil or butter if you think they need it, but don’t swamp the onions or the soup will become greasy. They should be coated and just glisten. Keep the heat at medium to start with until the onions have started to heat & fry.
Jake sticks his nose in
Don’t worry if your pan looks really full of onions – you’ll be surprised how much they will reduce down.
While the onions are frying, prepare your croutons. Heat your oven to 220C (200C fan). Slice the baguette quite thickly – you want to allow two to three croutons per portion, depending on how broad the baguette is. To make the croutons, you could toast, fry or grill them, but we find it easiest to put them in a hot oven. Place on a baking tray.
When the onions are just starting to soften, sizzle & fry (about 5 minutes), turn the heat down to low. Put the baguette slices into the hot oven, and set a timer for 30 minutes – this will time both the croutons & the onions. You’ll need to check & turn your croutons after about 15 minutes however.
You’ll need to stir the onions frequently through the frying time, so they brown evenly and don’t stick. What you are looking for is onions that are soft, golden and well-reduced, while still retaining some shape. See the third picture below. Ours today took about 45 minutes to get to this stage.
While the onions are frying and the croutons are baking, you can finish your preparation for the French onion soup. Chop some parsley, medium fine. See our herb Tip.
To prepare the thyme, remove the leaves from the woody stalks by pinching & running your fingers down them. The thyme doesn’t really need to be chopped, but we tend to give it a few snips with some scissors just to ensure no bits of stem remain.
Also grate the cheese to top the croutons. We like a mix of Gruyère and cheddar, but any medium-firm cheese you like will work. Grate enough to generously top each portion of soup.
When the croutons are about 15 minutes through their baking time, remove from the oven and drizzle with a little olive oil. Turn the croutons a few times in the oil to distribute it, ending up with the croutons turned onto their other side. Return to the oven for the next 15 minutes, or until crisp & golden.
Your preparation is done, and you are ready to make the French onion soup.
Making the French onion soup
Once the onions are cooked, the soup itself is very easy to make. Many recipes thicken the soup in some way – either adding a little flour to the onions, or a roux when the soup is simmering. Bibi didn’t and we don’t either. If you reduce the soup well, and don’t make it too wet to start with, the natural richness of the onions should make it thick enough. We also find there is enough body added by the croutons.
First add the stock to the onions, and stir well. We used about 700ml, or two packets, of liquid beef stock, but any stock you wish to use is fine. We also add a little white wine to our soup, as Bibi did and as is traditional, but it is not essential. Today we added about one large glass, or 250ml. If your soup does not look wet enough – and bear in mind it will reduce down further on cooking – add some boiling water. We like to rinse the stock packets out with it first.
Jake sticks his nose in
Some recipes use cider instead of wine – try this if you like the idea, it’s a nice combination, though we prefer the soup with wine. But alcohol isn’t essential if you don’t drink it – albeit the alcohol itself will burn off so the soup is safe for non-drinkers or children, if they are happy. Replace the wine with more stock or water if you prefer.
Turn the heat up under the soup so it starts to come to the boil. Now add the other key flavourings. We add a splash of cider vinegar, a tablespoon of the brown French mustard and the thyme (keep the parsley back for later).
Season well with black pepper, but don’t add salt at this stage. The stock is salty, and we also want the flavour of the soup to develop before we add more. You can taste the soup now (we do!), but bear in mind that the flavour will change & develop a lot on cooking, so we don’t tend to make any major adjustments yet. Bring the soup up to a rolling boil.
When the soup is boiling, turn the heat right down, and cover the pan with a lid. Cook for an hour, stirring occasionally. When the hour is up, taste the soup. Adjust any of the flavourings you feel you need to, until you like the taste. Today we added a splash more vinegar and another tablespoon of mustard. Stir the soup and cook a little longer so any added flavours can bed in. Today we cooked it for another 15 minutes.
Taste again, and adjust any final seasoning – today we added both more black pepper and a little salt. Also add a generous handful of parsley, leaving a little to garnish later.
Stir well. You can now carry on to finish the French onion soup, or you can keep the soup itself, covered (or in the fridge if keeping much longer than an hour or two), until you are ready to serve. If also keeping the croutons, wrap them or store them in in air-tight container.
Finishing & serving the French onion soup
French onion soup is traditionally served by placing the soup in bowls, adding the croutons & cheese and placing the bowls under a hot grill. This is also how Bibi did it. But we have two key watch-outs here. First, we find most grills inside domestic ovens are not very good. It’s also tricky to get the levels right to place the soup bowls high enough under the grill, and to get them in and out of the oven without spilling or dropping them.
But more materially, many soup bowls are not grill-proof. Even if they are oven-proof, they may not survive under a hot grill. We’re not convinced any of our current soup bowls are definitely grill-proof. And it would be a total disaster to have spent all this time and work making a lovely soup, only to have it explode under the grill! So only use this technique if you are certain your bowls are grill-proof.
So now we use another method – we simply bake the soup with the croutons in its casserole dish in a hot oven. It’s easier, safer and the result is just as good!
But more materially, many soup bowls are not grill-proof. Even if they are oven-proof, they may not survive under a hot grill. We’re not convinced any of our current soup bowls are definitely grill-proof. And it would be a total disaster to have spent all this time and work making a lovely soup, only to have it explode under the grill! So only use this technique if you are certain your bowls are grill-proof.
So now we use another method – we simply bake the soup with the croutons in its casserole dish in a hot oven. It’s easier, safer and the result is just as good!
To do this, first heat your oven to 220C (200C fan). While the oven is heating, bring the soup back to a gentle boil to warm it through. Once it is hot, add the croutons to the top in a single layer – they should float.
Now top very generously with the cheese, and place into the hot oven.
Bake until the cheese is nicely melted & bubbling a little – 10 to 15 minutes. Serve the French onion soup immediately in soup bowls, making sure each portion gets croutons, and ladling over more soup.
Garnish each portion with parsley.
We hope you enjoy your fabulous French onion soup!
Bibi’s Fabulous French Onion Soup
Ingredients
Equipment
Method
- Pre-heat the oven to 220C (200C fan). Peel & slice the onions, medium fine. See our onion Tip. Separate out the slices into a bowl.
- Add two generous knobs of butter and a good glug of olive oil to a hob-and-oven-safe casserole large enough to fit the onions & finished soup. Set over a medium heat until the butter melts. Add the onions, and stir to coat in the oil. Fry for a few minutes until they just start to soften with the heat medium. Then turn the heat down to low, and cook, stirring frequently, until the onions are soft, reduced and golden – at least 30 minutes and more like 45 minutes.
- While the onions are cooking, prepare the croutons. Slice the baguette quite thickly, allowing 2 to 3 slices per portion. Set on a baking tray and place into the hot oven for 30 minutes. About 15 minutes in, remove the croutons and sprinkle over a little olive oil. Rub the croutons in this and turn them over. Return to the oven for the rest of the cooking time, or until crisp & golden.
- While the onions & croutons are cooking, finish the preparation. Chop the parsley, medium. See our herb Tip. Remove the leaves from the thyme, and chop if needed. Grate both cheeses, enough to generously top the soup.
- When the onions are done, add the stock and white wine (if using). Stir and add a little boiled water if the soup looks too thick. Bring to the boil over a high heat. Add a splash of the cider vinegar, the thyme and 1 tablespoon of mustard. Season with pepper, but not with salt yet, and stir.
- When the soup is boiling, turn the heat down to low and cover with a lid. Simmer for one hour, stirring occasionally.
- When the hour is up, taste the soup and adjust with any of the flavourings until liked. Stir, and cook for another 15 minutes or so. Taste again, and season with salt & black pepper, if needed. Add the parsley, reserving some to garnish, and stir.
- You can now carry on to finish the French onion soup, or the soup itself can be kept, off the heat & covered, until you are ready to serve. Put in the fridge if keeping longer than a couple of hours. Also wrap or store the croutons in an air-tight container if making ahead.
- Pre-heat the oven to 220C (200C fan). Bring the soup just up to the boil to warm it through.
- Top the soup with the croutons in one layer. Also top generously with the grated cheese. Place into the hot oven until the cheese is melted & bubbling slightly – 10 to 15 minutes.
- Serve immediately, making sure each portion gets croutons, and ladling over more soup.
- Garnish with more parsley, and enjoy!
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