Though there are, of course, other onion soups (Iranian eshkeneh, for example, or Tuscan carabaccia), none has quite captured the international imagination like the “French” variety, said to have originated in the markets of Paris, where the rich, savoury broth fuelled early traders and late-night revellers alike. The accompanying mountain of molten cheese is optional, but strongly recommended.
Prep 15 min
Cook 2 hr 45 min
Serves 4 as a starter, 2 as a meal
80g butter, plus 2 tbsp extra for the toasts
3 sprigs thyme
1 tbsp plain flour
1 tbsp balsamic vinegar
400ml medium cider
600ml good-quality stock, preferably beef
1 garlic clove
100g gruyère or emmental
1 dash calvados or other brandy
1 Prepare the onions
Start by peeling and slicing the onions as thinly as possible; if you have one, a mandoline will make this task immeasurably easier and quicker. Note that, though pink Roscoff onions are the ideal here, ordinary yellow ones are fine; though I find white ones lack bite and red ones a bit too sweet, they, too, will work well enough.
2 Brown the onions
Melt the butter in a large, heavy-based frying pan on a medium-low heat. Add the onions, season, stir to coat with the fat, then turn down the heat and leave them to cook, stirring regularly, until a very deep, golden brown colour – you can turn up the heat a little once they’ve softened, but be very careful they don’t burn.
3 Keep browning the onions
Be warned that it will take at least an hour, and possibly more like two, to brown the onions sufficiently; don’t be tempted to rush it, or you’ll end up with bland or bitter soup, depending on whether you under- or overcook them. If you can’t stir them regularly, you may prefer to put them in an 180C (160Cfan)/350F/gas 4 oven for three hours instead.
4 Add the herbs and flour
Pick the leaves from the thyme and add to the pan with the flour (substitute cornflour if you need to keep the soup gluten-free).
Stir until well distributed, cook for another two minutes, then add the vinegar and a little of the cider, and scrape the bottom of the pan to dislodge any bits stuck to the base.
5 Add the cider and stock
Pour in the remaining cider, stirring as you do so, then add the stock. Beef stock is traditional here, and my own preference, because I find it has a depth of savoury flavour that other stocks struggle to match, and works particularly well with the sweetness of onions. Use good chicken or vegetable stock, if you prefer, or even water with a hefty spoonful of Marmite or miso paste to give it some oomph.
6 Simmer for an hour
Turn up the heat and bring the contents of the pan up to a simmer, then reduce it slightly and leave the soup to bubble away gently for about an hour, stirring occasionally to prevent the onions sticking. Towards the end of the cooking time, if you’re planning to eat the soup immediately, start preparing the croutons.
7 Make the croutons
Cut eight thin slices from the baguette and melt a couple of tablespoons of butter in a small pan (or in the microwave).
Heat the grill and put the bread slices on a baking tray. Cut the garlic cloves in half and run the cut side over the bread, then brush the bread with melted butter. Grill until golden, then turn over to toast the other side. Remove the bread, and leave the grill on.
8 Now for the cheese
Grate the cheese; the nutty flavour of gruyère is my favourite here, but emmental, cheddar or anything with good melting capabilities will work.
Add the brandy to the soup, and check and adjust the seasoning, if necessary. Ladle into ovenproof bowls and top each with two croutons and a mound of cheese. Grill until the cheese is molten and bubbling, and serve at once.
9 Finishing touches
If you get to step 8 and find your soup lacks a certain something, even after you’ve adjusted the seasoning (which can happen if your onions or stock are deficient in the flavour department), try stirring in an umami-rich ingredient such as Marmite, Bovril, miso paste or fish sauce, then taste and add more as necessary, until it hits the spot.