Deeply caramelized onions simmered in beef broth and topped with toasted bread and melted gruyere, France's classic bistro soup.
French onion soup depends almost entirely on one technique done well: caramelizing a large quantity of onions low and slow until they turn a deep mahogany brown, a process that can't be rushed without sacrificing the soup's signature depth. Once the onions collapse into a sweet, jammy base, a splash of wine deglazes the pot before beef stock and fresh thyme go in to simmer into a rich, dark broth that tastes far more complex than its short ingredient list suggests. The finishing touch — a thick slice of toasted baguette floated on top and buried under melted gruyere, then broiled until bubbling and browned — turns the soup into a full meal, the cheese pulling into long strands with every spoonful.
Serves 4
Melt butter with olive oil in a heavy pot, add onions, sugar and salt, and cook over medium-low heat, stirring occasionally, for 45-50 minutes until deeply browned and jammy.
Resist the urge to raise the heat to speed this up — true caramelization takes time, and rushing it just burns the onions instead of sweetening them.
Pour in the white wine, scraping up any browned bits from the bottom of the pot, and cook 3 minutes.
Add beef stock, bay leaves and thyme; bring to a simmer and cook uncovered 25-30 minutes to let the flavors meld.
Remove the bay leaves and thyme sprigs, and adjust salt to taste.
Ladle the soup into oven-safe bowls, float a slice of toasted baguette on top, and pile with grated gruyere.
Broil until the cheese is melted, bubbling and browned in spots, about 3-5 minutes, watching closely.
Caramelize the onions truly slowly — 45 minutes is the minimum for proper depth, and rushing with high heat produces bitter, unevenly browned onions instead.
Use a good quality beef stock, since it's the main liquid flavor in the soup and any weakness there will be obvious.
Broil the bowls on a sturdy baking sheet and watch closely — the cheese can go from perfectly melted to burnt within a minute under the broiler.
A vegetarian version uses a rich vegetable or mushroom stock instead of beef stock.
Comte or Swiss cheese can substitute for gruyere if it's not available.
Some versions add a splash of cognac along with the wine for extra depth.
Refrigerate the soup (without the bread and cheese topping) up to 4 days, or freeze up to 3 months; add fresh toasted bread and cheese and broil again just before serving.
French onion soup has roots as a simple peasant dish going back centuries, but its modern form with the toasted bread and melted cheese became widely popularized in Parisian bistros and market restaurants during the 19th and 20th centuries.
Yes, caramelized onions keep refrigerated for up to a week, so you can prepare them in advance and assemble the soup quickly on the day.
Toast the bread and melt the cheese separately under the broiler on a tray, then float the cheesy toast on top of the soup in a regular bowl.
They were likely cooked at too high a heat, which burns the sugars instead of caramelizing them slowly — lower the heat and be patient.
Per serving (400g / 14.1 oz) · 4 servings total
Ask our AI cooking assistant anything about this recipe — substitutions, techniques, scaling.
Chat with AI Chef →Join the conversation
Sign in to leave a comment and save your favourite recipes
Have feedback or need help?
We read every email and reply within 1–2 business days.
© 2026 MyCookingCalendar. All rights reserved.
