French Onion Soup, my childhood favourite type.

Soupe à l’oignon gratinée: the soup of the Paris market workers, the late-night revellers, and anyone who has ever needed something deeply restorative. The onions take an hour. Nothing else does.

There is a particular kind of evening that calls for French onion soup. Cold enough to mean it. A week that has asked more of you than you agreed to. The desire for something that smells extraordinary from the other side of the kitchen, that arrives at the table still bubbling at the edges, that requires a moment of breaking through the crust before you can get to the dark, savoury broth beneath. It is a dish with theatre, with warmth and with the kind of depth that only comes from unhurried cooking. And it rewards patience so thoroughly that the patience stops feeling like effort.

French onion soup began, as so many great things do, as the food of people who didn’t have much. In medieval France it was soupe des pauvres — the soup of the poor — built on onions because onions were cheap, abundant and sustaining in a way that stretched a small amount of everything else.

The dish found its modern form in the bistros and brasseries around Les Halles, the great covered market of Paris, in the eighteenth and nineteenth centuries. These were establishments that stayed open through the night, serving the market porters, coachmen and night watchmen who needed cheap, hot food at hours when most of the city was asleep. The soup they were serving was simple enough: onions, broth, bread. What changed it into the dish we know now was the addition of a thick blanket of Gruyère, pushed under a grill until it blistered and bubbled. Those restaurants — Au Pied de Cochon, La Poule au Pot, Chez Baratte — took a soup of the poor and made it extraordinary, and in doing so they created the Gratinée des Halles, the dish that would eventually become French onion soup to the rest of the world.

The gratinée became, in time, simultaneously breakfast for the market workers, supper for the party crowd emerging blinking from the cabarets, and a widely celebrated hangover remedy, earning it the rather wonderful nickname la soupe des ivrognes — the soup of drunks. It is a dish that has always belonged to everyone, from the forts des Halles hauling crates through the pre-dawn dark to the well-dressed diner at Maxim’s, and this classlessness is part of what makes it so enduringly good. Au Pied de Cochon still serves it. Twelve euros or thereabouts, at three o’clock in the morning, to anyone who needs it.

There are very few components in French onion soup and all of them matter, which means there is nowhere to hide.

The onions are the entire point. Six large ones, more than you expect, because they cook down to a fraction of their raw volume over the long, slow caramelisation. And the caramelisation cannot be shortened, not honestly. Forty-five minutes at minimum, ideally closer to an hour, over medium-low heat. The onions need to go from sharp and white to sweet and the colour of dark honey, releasing their natural sugars slowly until the whole pan smells like something wonderful. Rushing it produces soft, pale onions that taste only of themselves rather than of everything they can become. The temptation to turn up the heat is almost constant. Don’t.

The stock is the other half of the dish. A good, dark, gelatinous beef stock — the kind that sets in the fridge overnight — makes a soup that tastes of something. A thin or over-salted shop-bought stock makes a soup that tastes of salt and not much else. If you make your own stock with any regularity, this is the recipe to make it for. If you don’t, find the best you can: a butcher’s own, or a reduced liquid stock from a decent brand rather than a cube. The quality of the broth is not a place to economise.

The deglazing matters more than most recipes admit. After the onions are properly caramelised, the bottom of the pan is covered in a dark, sticky layer of browned sugars called the fond. This is concentrated flavour, and it all goes into the soup the moment you pour in the wine and scrape. Use a wooden spoon and scrape thoroughly. Dry vermouth works particularly well here, a little sharper and more herbal than white wine, and it gives the finished soup a faint botanical quality that sits beautifully against the sweetness of the onions.

Then there is the Gruyère. Do not substitute. Gruyère melts in the particular way that gives the gratinée its blistered, pulling, golden-edged crust, and no other cheese quite replicates it. Buy it in a piece and grate it coarsely yourself; pre-grated Gruyère from a bag melts differently, with less pull and less drama, and the drama is rather the point.

Serves 4. About 20 minutes’ active work, an hour of patient cooking, and 5 minutes of grill time.

Ingredients

For the soup

• 50g unsalted butter
• 1 tbsp olive oil
• 6 large onions, finely sliced (yellow or white, not red)
• 1 tsp fine sea salt, plus more to season
• 1 tsp caster sugar
• 3 garlic cloves, finely sliced
• 1 tbsp plain flour
• 200ml dry white wine or dry vermouth
• 1.5 litres good beef stock
• 4 fresh thyme sprigs
• 2 bay leaves
• Black pepper, freshly ground

For the gratinée

• 1 baguette, cut into thick slices
• 200g Gruyère, coarsely grated

1. The long caramelisation. Melt the butter with the olive oil in a large heavy-based pan or Dutch oven over medium-low heat. Add the onions and salt, stir to coat, and cook slowly, stirring every 5 to 10 minutes, for 40 to 60 minutes until the onions are a deep, even golden brown and smell sweet and concentrated rather than sharp. Do not rush this. If they catch and start to stick, add a small splash of water and scrape the bottom. The colour you are aiming for is dark honey, not pale gold.

2. Add the sugar and garlic. Once the onions are deeply caramelised, stir in the sugar and the garlic and cook for a further 2 minutes until the garlic is soft and fragrant.

3. Flour and deglaze. Stir in the flour and cook for 1 minute. Pour in the wine or vermouth and use a wooden spoon to scrape every last bit of the fond — the dark, sticky residue — from the bottom of the pan. Let it bubble and reduce for 2 to 3 minutes until the sharp smell of alcohol has softened. This step is where the depth of the soup lives.

4. Build the soup. Pour in the stock, add the thyme sprigs and bay leaves, and bring to a gentle simmer. Cook uncovered for 20 to 30 minutes. Remove the thyme and bay leaves, then taste and season generously with black pepper and more salt as needed. The soup should taste deeply savoury, sweet and complex. If it tastes flat, it needs more salt. If it tastes thin, let it reduce a little further.

5. Toast the croutons. Heat the oven to 180°C (160°C fan). Lay the baguette slices on a baking tray and bake for 10 to 12 minutes until completely dry, golden and crisp all the way through. A wet crouton collapses in hot soup almost instantly; a properly dried one holds long enough to matter.

6. Assemble and gratinée. Heat your grill to its highest setting. Ladle the soup into deep, ovenproof bowls set on a baking tray — this makes the next step much safer. Float one or two croutons on each portion, then cover generously with the Gruyère, right to the edges so it seals the bowl. Slide under the grill for 3 to 5 minutes until the cheese is bubbling, blistered and beginning to brown at the edges. Watch it. The line between golden and burnt moves quickly and without warning.

7. Serve immediately. Carry the bowls straight to the table. Warn people it is very hot. The cheese will keep bubbling for a minute or two, and the first spoonful, breaking through the crust into the dark broth below, is what this dish is entirely about.

On the onions: yellow or white onions are the ones to use. Red onions caramelise beautifully in other contexts but turn an unappetising purple-grey in this soup and add a sweetness that tips over into cloying. The quantity — six large — will look alarming raw. It is correct. They reduce to a fraction of their volume in the pan, and a soup with too few onions is a soup without a purpose.

On the timing: this is a recipe that rewards the make-ahead approach. The soup base keeps in the fridge for three days and genuinely improves overnight, as the flavours deepen and settle. The gratinée, however, should always be done fresh and immediately before serving: assembled croutons and Gruyère left standing lose their structural integrity and arrive at the table soft rather than crackling.

On the bowls: you need ovenproof ones with depth. Wide, shallow bowls let the crouton spread, the cheese runs off the edges and you lose the sealed, oven-hot crock effect that makes the gratinée what it is. French bistro lion-head crocks are the traditional choice and not without reason. A deep ramekin in a pinch does the same job.

On the wine versus vermouth question: both work. Dry vermouth gives the soup a slightly more herbal, complex quality that I find particularly good with the sweet onions. A dry white wine is perfectly correct and perhaps more versatile. What you should not use is something sweet, something oaky, or something you would not also pour a glass of.

On what to serve alongside: this is a complete meal in a bowl and needs almost nothing. Good bread on the table, more than you think, because the broth is worth pursuing to the end. A green salad dressed sharply if you want a second course. And something cold to drink: a glass of the wine you used in the soup, or a light red if the evening demands it.

This is my own recipe, made many times through winters in varying states of patience, always rewarded. Not a paid or gifted feature.