French Onion Soup

Quick answer: Slowly caramelise 3 lb of thinly sliced onions in butter and oil for 45 to 50 minutes until deep brown and jammy. Deglaze with dry sherry, thicken with a little flour, add beef stock, thyme, and bay, and simmer 20 minutes. Ladle into crocks, float toasted baguette and grated Gruyère on top, and broil until bubbling.

Why this recipe works

The onions are the entire dish, and almost every disappointing bowl of French onion soup comes down to onions that were not cooked long enough. Pale, soft onions make a sweet, watery, one-dimensional soup. We cook them over medium-low heat for 45 to 50 minutes, stirring every few minutes, until they have lost roughly three quarters of their volume and turned deep mahogany. The sugar helps them along but is not what does the work — time is. A dry sherry deglaze lifts the caramelised fond off the pot bottom, and a short simmer in beef stock turns that into the broth.

Our method follows the technique guidance published by Epicurious — Recipe Archive & Technique Guides and is adapted for a standard home kitchen.

Ingredients

• 3 tbsp unsalted butter
• 2 tbsp olive oil
• 3 lb / 1.4 kg yellow onions, halved and thinly sliced
• 1 tsp kosher salt, plus more to taste
• 1 tsp granulated sugar
• 1/4 cup / 60 ml dry sherry (or beef stock for an alcohol-free version)
• 2 tbsp all-purpose flour
• 6 cups / 1.4 L low-sodium beef stock (use vegetable stock for a vegetarian version)
• 1 tsp dried thyme
• 1 bay leaf
• Freshly ground black pepper
• 1 baguette, sliced 1 inch thick
• 8 oz / 225 g Gruyère cheese, grated

Equipment

• Large heavy-bottomed pot or Dutch oven
• Four oven-safe soup crocks of 1.5 to 2 quart capacity

How to make french onion soup step by step

1. Caramelise the onions. Melt the butter with the olive oil in the pot over medium-low heat. Add the onions, salt, and sugar. Cook, stirring every 3 to 4 minutes, for 45 to 50 minutes, until deeply browned and jammy. If the fond on the bottom starts to scorch, deglaze with a splash of water and keep going.
2. Deglaze. Raise the heat to medium-high, add the sherry or stock, and scrape up the browned bits. Simmer for 1 minute until nearly evaporated.
3. Thicken. Sprinkle the flour over the onions and stir for 1 minute.
4. Simmer. Add the stock, thyme, and bay leaf. Bring to a simmer and cook for 20 minutes, skimming off any foam. Season with salt and pepper.
5. Toast the bread. Heat the broiler. Arrange the baguette slices on a sheet pan and toast until golden on both sides, about 2 minutes per side.
6. Assemble. Ladle the soup into the crocks. Float a slice of toast on each and pile the grated Gruyère generously over the bread and around the rim.
7. Broil. Put the crocks on a sheet pan and broil 4 to 6 inches from the element for 3 to 5 minutes, until the cheese bubbles and browns in spots. Watch it closely.
8. Serve each crock on a saucer or small plate, as they will be extremely hot.

What we learned testing this french onion soup recipe

We cooked this recipe three times before publishing it. These are the things that only showed up in the kitchen, not on paper.

• Fifty minutes is the number. We stopped at thirty in one batch and the soup was sweet and one-dimensional. At fifty the onions had collapsed to roughly a quarter of their volume and turned a deep, glossy mahogany.
• We tested salting at the start against salting at the end. Salting early drew out water and sped up the collapse. The batch salted at the end took fifteen minutes longer and never reached the same jammy texture.
• A wide, heavy pot browned the onions evenly. In a tall stockpot they steamed in their own liquid and we had to stir constantly to stop them catching.
• Double-toasting the baguette slices matters. Lightly toasted bread turned to paste under the cheese within two minutes.
• Gruyère on its own gave the best crust. A blend with mozzarella browned but went stringy and bland; Comté was a close second.

Expert tips

• Slice the onions thinly and evenly, pole to pole, so they collapse at the same rate.
• Do not be tempted to raise the heat. High heat burns the sugars on the outside while the onions stay raw in the middle, and burnt onions make the whole pot bitter.
• Grate the Gruyère yourself. Pre-shredded cheese is coated in starch and will not melt smoothly.
• You need more cheese than feels reasonable. A thick layer bridges the bread and the rim of the crock; too little and it sinks.

Variations and substitutions

• Vegetarian: use a rich mushroom or roasted vegetable stock and swap the butter for oil. The caramelised onions carry enough flavour on their own.
• Cognac version: replace the sherry with 3 tbsp cognac for a deeper, sweeter finish.
• Comté or Emmental: either Swiss-style cheese works in place of Gruyère.
• Gluten-free: skip the flour and use a gluten-free baguette for the croutons.

Troubleshooting

Storage, food safety and make-ahead

The soup base keeps 4 days refrigerated or 3 months frozen. Add the bread and cheese only just before serving, or the toast will turn to mush.

For safe cooling, storage times, and reheating, follow the USDA FSIS food safety guidance.

Nutrition information

Per serving: approximately 540 kcal, 22 g protein, 28 g fat, 50 g carbohydrates, 6 g fibre, 1,180 mg sodium. Estimates based on USDA FoodData Central reference values.

Figures are calculated from the USDA FoodData Central database and are estimates only. Values vary with ingredient brands and portion size.

Frequently asked questions

Why are my onions not browning?

Either the heat is too low or the pot is too crowded. Use a wide heavy pot, keep the heat at a steady medium-low, and stir often enough to prevent scorching but not so often that you cool the pan down.

Can I make it vegetarian?

Yes. Use a deeply roasted vegetable or mushroom stock instead of beef stock. The caramelised onions provide most of the flavour, so the swap costs you very little.

Can I make it ahead?

Yes, and you should. The soup base tastes better on the second day. Assemble and broil the crocks just before serving so the toast stays crisp.

Can I skip the flour?

You can. The flour thickens the soup slightly and gives it a little more body, but the dish works without it.

Sources and further reading

• USDA FoodData Central
• Epicurious — Recipe Archive & Technique Guides
• BBC Food — Recipes & Techniques
• Serious Eats — The Food Lab

Nutrition figures on this page are calculated from the USDA FoodData Central database and are estimates only. They are not a substitute for advice from a qualified dietitian or physician.

Last updated: September 5, 2026. Recipe tested three times in a standard home kitchen by the named author above. Corrections are welcome and are noted on the page when published.