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Felicity's perfect french onion soup
Felicity's perfect french onion soup. Photograph: Felicity Cloake
Felicity's perfect french onion soup. Photograph: Felicity Cloake

How to cook perfect french onion soup

Rich and warming, this is a dish to make while the last gasp of winter is in the air. Which other bistro classics are worthy of revival?

I had bizarre tastes as a child. I turned my nose up at fish, but would greedily devour their eggs as Sindy-pink taramasalata. I loved that processed smoke-flavoured cheese that looked like a sausage, and my favourite restaurant treat, at the age of eight, was french onion soup. To be honest, this last probably had more to do with the monstrous garnish of melted Gruyère than the richly sweet and savoury broth beneath, but nevertheless, I enjoyed every last slurp.

My tastes are broader these days, and I haven't had any of the above in ages – mainly because, for reasons of sustainability, taste and fashion respectively, they're rarely on offer. Onion soup, however, is worth reviving: and quickly, because, beefy, boozy and pungent, it's very much a cold-weather dish. Make it now, before you lose your chance to really enjoy it for another year.

Know your onions

Spanish and yellow onions
Spanish and yellow onions. Photograph: Felicity Cloake

As Anthony Bourdain observes in the Les Halles Cookbook "onion soup, unsurprisingly, is all about the onions." Like most of the recipes I find, however, he doesn't make any specific recommendations on this point: only Raymond Blanc delves into the matter further, explaining that "the quality of the onions is vital ... we want both high acidity and high sugar levels to create a fully flavoured soup. The best onions are Pink Roscoff. Spanish onions, although lacking in acidity, will also work."

Although I make a tour of the greengrocers of north London, no one stocks these Breton specialities (which, I later discover are in fact available online - what isn't?) so I settle for Spanish onions instead. As Raymond observes, they do indeed lack acidity – despite long caramelisation, his soup seems distinctly less onion-y than the others, which defeats the point. I'd be interested to try the famous Roscoff, but ordinary yellow onions seem quite adequate for the purpose.

Bourdain is more interested in how those onions are cooked, stressing that they must be "a nice, dark even brown colour". In the grand tradition of chefs, he is cheerfully dishonest about how long this will take: if anyone has achieved this level of caramelisation in 20 minutes, I'd like to hear from you. In my experience, it takes at least twice that, and usually well over an hour.

Thomas Keller 5 hour caramelised onions
Thomas Keller 5 hour caramelised onions. Photograph: Felicity Cloake

Thomas Keller, the notoriously perfectionist chef of California's Michelin-starred The French Laundry, and New York's equally decorated Per Se, would have Bourdain for breakfast: his onions are cooked very gently for five hours (yes, that's five hours of regular stirring), until they're the colour of ... well, as one blogger put it, "poop". Sadly true, but they taste amazing: crunchy and sugary, and so very delicious that I end up eating them like crisps, pinching a few from the bowl each time I pass. They give the soup an intense sweetness: in fact, I think Keller's soup is a little too sweet – there's no oniony bite there.

Michel Roux Jr demands only that the onions are "soft, but still in slices", estimating a cooking time of about 30–40 minutes in the Le Gavroche Cookbook. Although they have begun to caramelise, they're nowhere near the "deep golden brown" demanded by Lindsey Bareham and Simon Hopkinson in The Prawn Cocktail Years and it shows in the results – the soup lacks that lovely sweet heat which is the happy middle ground I'm aiming for. Nut brown and soft rather than desiccated onions seem to be the ideal.

(In the recipe in A Celebration of Soup, Lindsey suggests adding a pinch of sugar to the onions to help the caramelisation, although she and Simon decry this as a trick of "cowboy" trick in The Prawn Cocktail Years, pointing out that "onions have a high sugar content and will exude their own sweetness as they sweat". I agree it's unnecessary, having tried it, but there doesn't seem any harm in adding a little soft brown sugar at the end if you feel your onions aren't quite as sweet as they ought to be.)

Stocking up

Thomas Keller recipe french onion soup
Thomas Keller recipe french onion soup. Photograph: Felicity Cloake

Soup, of course, should be wet, and the liquid element will have a significant effect on the character of the finished dish. Beef stock is the most common choice, used by Michel Roux Jr, Simon Hopkinson and Lindsey Bareham, Nigel Slater, Thomas Keller and innumerable others, but there are dissenters.

Ever the rebel, Anthony Bourdain opts for chicken stock, while, perhaps in obedience to the dish's peasant roots, Raymond Blanc uses good old water. The results confirm my long held opinion that, just because something's authentic, it doesn't make it the best choice: Raymond's soup is underwhelming: sweet, but without much savoury depth. Bourdain's is much, much nicer, but I miss the beefy richness that marries so well with onions (see also, steak and onion crisps). It does need to be good stock though: as the backbone of the soup, the powdered stuff just won't wash. If it doesn't wobble, then it isn't up to scratch

Booze

Raymond Blanc recipe french onion soup
Raymond Blanc recipe french onion soup. Photograph: Felicity Cloake

More wetness is provided by the inclusion of some sort of alcohol. Raymond and Simon and Lindsey both stick to the classic white wine, although the Prawn Cocktail Years authors also give the option of using cider instead. The Le Gavroche recipe just specifies cider, while Anthony Bourdain climbs out on another limb with port.

I think the robustly flavoured cider works best with the onions (especially as the famed Roscoff version so loved by Raymond hails from cider-glugging Brittany) – but I love the sweetness that Bourdain's port brings, so I've gone for a medium-dry incarnation instead of Roux Jr's dry version. I like the calvados he adds at the end too: like Simon and Lindsey's Cognac, it adds an unmistakably Gallic kick to ingredients that are otherwise fairly pan-European.

To roux or not to roux?

Anthony Bourdain recipe french onion soup
Anthony Bourdain recipe french onion soup. Photograph: Felicity Cloake

Most onion soup recipes, I'm surprised to discover, use flour as a thickener, whether in the form of a roux whisked into the stock, as in the Le Gavroche and the Prawn Cocktail Years recipes, or by stirring the flour into the onions and then making the roux directly in the pan, as Raymond Blanc does. Only Anthony Bourdain eschews it, but I like a slightly thicker soup: it seems to fit with the hearty character of the dish as a whole and, as I don't have a kitchen porter to do my washing up, I'm opting for Raymond's one-pot method.

Other ingredients

Michel Roux Jr recipe french onion soup
Michel Roux Jr recipe french onion soup. Photograph: Felicity Cloake

Vinegar is a popular addition to onion soups, contributing, as Michel Roux Jr puts it, a slightly "sweet and sour" taste. He, like Thomas Keller, uses sherry vinegar, but if they're going to go for a Spanish product, then I feel justified in opting for Bourdain's balsamic instead – its richly caramelised flavour is perfect with the onions.

I'm not sure about his use of lardons though: although bacon always gets on famously with both onions and cider, it changes the character of the dish. I want onions to be the only solid ingredient in my soup: let them be the stars of the show for once.

Le Gavroche serve their soup with an egg yolk and a tablespoon of crème fraîche whisked into it, but, although I can see the richness going down well in that hushed dining room on Upper Brook Street, it's too much when the soup is served in the kind of inelegant (aka "rustic") portions it really deserves to be.

The toast with the most

Prawn Cocktail Years recipe french onion soup
Prawn Cocktail Years recipe french onion soup. Photograph: Felicity Cloake

Most important of all, of course, are those glorious cheese toasts. Simon and Lindsey make theirs in advance, cheese and all, and then retoast them, presumably to create a sturdier raft. I agree that the bread should be toasted before being topped with cheese to slow the sogging process, as Bourdain and Roux Jr prefer, and I like the idea of rubbing it with garlic, as the Prawn Cocktail Years authors suggest (just in case all those onions weren't allium enough). And remember, if you can see soup beneath, then you need more cheese.

Perfect french onion soup

Felicity's perfect french onion soup
Felicity's perfect french onion soup. Photograph: Felicity Cloake

Serves 4 as a starter

80g butter, plus a little extra for the toasts
4 onions, peeled and thinly sliced
1 tbsp plain flour
3 sprigs thyme, leaves picked
1 tbsp balsamic vinegar
400ml medium cider
600ml good-quality beef stock
Dash of calvados or other brandy
8 slices of baguette
1 clove of garlic, halved
100g Gruyère, grated

1. Melt the butter in a large, heavy bottomed pan over a low heat. Add the onions, season and cook, stirring regularly, until caramelised and deep brown. (Once they've softened, you can turn up the heat a little, but keep an eye on them.) This will probably take between 90 minutes to 2 hours, depending on your nerve.

2. Stir in the flour and thyme and cook for a couple of minutes, stirring, then add the vinegar and a third of the cider, stirring and scraping all the brown bits from the bottom of the pan. Whisk in the rest of the cider and the stock, and bring to the boil. Simmer for about an hour. Meanwhile, heat the grill and rub the baguette slices with the cut side of the garlic clove. Brush with melted butter, and toast on both sides.

3. Add the brandy to the soup and check the seasoning. To serve, ladle into ovenproof dishes and top with 2 croutons and a mound of cheese. Grill until golden, then serve immediately.

Do you miss french onion soup? Why has it fallen from fashion (indeed has it: does anywhere still serve a decent version?) and what's your secret? Which other bistro classics have been unjustly neglected?

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