Classic French Onion Soup
Deeply caramelised onions in a savoury broth, topped with toasted baguette and a melted blanket of Gruyere.
Using a good vegetable stock keeps this suitable for vegetarians without losing any depth, especially if you add a spoonful of miso or soy sauce for the savoury bass note that beef broth would normally supply. A splash of dry white wine and a few thyme sprigs do the rest.
The topping is what people remember: a slice of baguette floated on the soup, buried under Gruyère and grilled until it bubbles and browns. Broil the bowls close to the element and watch them, because the line between beautifully blistered and burnt is about thirty seconds wide.
Ingredients
- 1 kg yellow onions, peeled and sliced about 3 mm thick
- 50 g unsalted butter
- 1 tbsp olive oil
- 1 tsp fine salt, plus more to taste
- 1 tsp sugar
- 1 tbsp plain flour
- 120 ml dry white wine
- 1.2 litres good vegetable stock
- 1 tbsp white miso or soy sauce
- 2 sprigs fresh thyme, or 1/2 tsp dried
- 1 bay leaf
- 1/2 tsp black pepper
- 8 slices baguette, cut 2 cm thick
- 150 g Gruyère, grated
- 1 garlic clove, halved
Instructions
- Melt the butter with the olive oil in a heavy, wide pot over medium-low heat. Add the onions, salt and sugar and stir to coat.
- Cook the onions uncovered for 40-45 minutes, stirring every few minutes and scraping up the browned bits. They should end up soft, jammy and a deep golden brown. If they catch, lower the heat and add a splash of water.
- Sprinkle over the flour and stir for 1 minute, then pour in the wine and let it bubble for 2 minutes, scraping the base clean.
- Add the stock, miso or soy sauce, thyme, bay leaf and pepper. Bring to a simmer, then cook gently for 15 minutes. Taste and adjust the salt — the miso and cheese are both salty, so go carefully. Remove the thyme stems and the bay leaf.
- While the soup simmers, toast the baguette slices until crisp, then rub one side of each with the cut garlic clove.
- Heat the grill to its highest setting. Ladle the soup into four ovenproof bowls and float two baguette slices on each.
- Pile the grated Gruyère over the bread, covering it right to the rim of the bowl.
- Grill for 3-5 minutes, close to the element, until the cheese is melted, bubbling and spotted golden brown. Serve straight away — the bowls are very hot.
Cook’s tips
- Do not rush the onions. Anything faster than 40 minutes gives you pale, sharp onions rather than sweet caramelised ones.
- Slice the onions evenly, about 3 mm, so they all soften at the same rate.
- Fill the bowls only two-thirds full so the bread and cheese have room to sit above the liquid.
- Set the bowls on a baking tray before they go under the grill — hot soup sloshes.
- If you have no ovenproof bowls, grill the loaded bread on a tray and slide it onto the soup at the table.
Substitutions
- Comté, Emmental or a vegetarian hard cheese all melt well in place of Gruyère.
- Sourdough or country bread works if you have no baguette.
- Dry cider can stand in for the white wine.
- For a vegan version use olive oil, skip the cheese and top the toast with a thick cashew cream and a sprinkle of nutritional yeast.
Storage & reheating
The soup base keeps in the fridge for 4 days or freezes for 3 months — freeze it without the bread and cheese. Reheat gently on the stovetop and add the topping just before serving.
FAQ
Can French onion soup be vegetarian?
Yes. The only non-vegetarian element traditionally is beef stock, so use a good vegetable stock with a spoonful of miso or soy sauce for savoury depth. Gruyère is made with animal rennet, so choose a vegetarian-certified hard cheese if that matters to you.
Why is my onion soup not brown?
The onions were cooked too quickly or not long enough. They need 40-45 minutes over medium-low heat to caramelise properly — browning the flour or adding a dash of soy sauce cannot replace that.
Can I make it ahead for guests?
Yes, and it is better that way. Cook the soup base up to 3 days ahead, then reheat, top with bread and cheese and grill just before serving.
