Few things feel cozier than a bowl of French onion soup—silky, deeply caramelized onions floating in a rich broth, capped with golden, bubbling Gruyère toasts. This version keeps the bistro flavor you love but breaks each step down so it’s approachable for any home kitchen.
Why This Recipe Works
Slowly cooking the onions until they’re deeply browned builds the soup’s signature sweetness and complexity. Deglazing with wine loosens all those flavorful browned bits, while a mix of beef stock and herbs gives the broth body. Finally, thick slices of toasted bread act as a raft for nutty Gruyère, which melts and browns under the broiler for that classic, cheesy lid.
Ingredients
For the Soup
- 3 tbsp unsalted butter
- 1 tbsp olive oil
- 4–5 large yellow onions (about 1.5–2 lb / 700–900 g), thinly sliced pole‑to‑pole
- 1 tsp salt (plus more to taste)
- ½ tsp sugar (optional, helps browning)
- 2 cloves garlic, minced
- 2 tbsp all‑purpose flour
- ½ cup beef stock mixed with 1–2 teaspoons apple cider vinegar or white wine vinegar
- 6 cups (1.4 L) good beef stock (or half beef, half chicken)
- 2 tsp Worcestershire sauce (optional but adds depth)
- 2 sprigs fresh thyme (or ½ tsp dried)
- 1 bay leaf
- Freshly ground black pepper
For the Gruyère Toasts
- 1 baguette or small crusty loaf, cut into ½–¾ inch (1.25–2 cm) slices
- 1–2 tbsp olive oil (or soft butter)
- 1 cup (about 100 g) grated Gruyère cheese (or a mix of Gruyère and Swiss/Comté)
- Optional: 2 tbsp freshly grated Parmesan, for extra sharpness
Equipment Needed
- Large heavy pot or Dutch oven
- Wooden spoon
- Oven‑safe soup bowls or ramekins (broiler‑safe)
- Baking sheet
- Ladle
Step‑by‑Step Instructions
1. Slice and Start the Onions
Peel the onions, cut them in half from root to tip, then slice them into thin half‑moons. Aim for even thickness so they cook uniformly.
Heat butter and olive oil in a large Dutch oven over medium heat. Add all the sliced onions, sprinkle with 1 teaspoon salt and the sugar if using, and toss to coat. The pot will look very full—this is normal; they’ll cook down dramatically.
2. Slowly Caramelize the Onions
Cook the onions over medium to medium‑low heat, stirring every few minutes so they soften and release moisture. As they start to shrink, switch to more frequent stirring and adjust the heat so they slowly turn from pale golden to deep amber without scorching.
This stage typically takes 35–45 minutes, depending on your pot and stove. If brown bits begin to form on the bottom before the onions deepen in color, add a tablespoon of water and scrape with the wooden spoon to dissolve them back into the onions.
You’re looking for very soft onions that have lost most of their volume and are a rich caramel color, not just yellow.
3. Add Garlic and Flour
Once the onions are deeply caramelized, stir in the minced garlic and cook for 30 seconds until fragrant—no longer, or it may burn.
Sprinkle flour over the onions and cook for 1–2 minutes, stirring constantly. This lightly toasts the flour and helps thicken the broth so it has that velvety restaurant texture instead of feeling watery.
4. Deglaze with Stock
Pour in ½ cup beef stock (or beef stock mixed with a little vinegar), scraping the bottom of the pot with your spoon to loosen all the browned bits. Let it simmer for 2–3 minutes until slightly reduced and the fond is dissolved into the onions.
5. Build and Simmer the Broth
Add the beef stock, Worcestershire (if using), thyme sprigs, and bay leaf. Stir well, bring to a gentle simmer, then reduce heat to low.
Let the soup simmer, uncovered, for 20–30 minutes so the flavors meld and the broth thickens just a touch. Taste and adjust seasoning with salt and black pepper as needed; beef stocks vary widely in saltiness, so don’t add extra salt until the end.
Before serving, fish out the thyme stems and bay leaf.
6. Prepare the Gruyère Toasts
While the soup simmers, preheat the oven to 375°F (190°C). Arrange baguette slices on a baking sheet in a single layer. Lightly brush both sides with olive oil or spread thinly with butter.
Toast in the oven for about 8–10 minutes, flipping once, until dry and lightly golden at the edges. The bread should be sturdy enough to sit on top of hot soup without immediately falling apart.
If you like garlic, you can rub the warm toasts gently with a cut clove of garlic as they come out of the oven.
7. Assemble and Broil
Ladle hot soup into oven‑safe bowls, leaving a little room at the top. Float 1–2 toasted slices on each bowl, covering most of the surface. Pile grated Gruyère generously over the bread, and sprinkle with Parmesan if desired.
Place the bowls on a baking sheet (for easier handling) and set under the broiler on high. Broil for 2–4 minutes, watching closely, until the cheese is melted, bubbling, and spotted deep golden brown.
Carefully remove from the oven—the bowls will be extremely hot.
8. Rest Briefly and Serve
Let the soups rest for 3–5 minutes so the bubbling subsides and the cheese sets slightly. Serve on small plates or saucers to protect the table, warning everyone about the hot bowls.
The best way to eat French onion soup is to break through the cheesy toast with a spoon, scooping broth, onions, and gooey cheese in each bite.
Pro Tips
- Take your time with the onions. Truly caramelized onions are deep golden-brown and jammy, not just soft and translucent; plan on 35–45 minutes over medium‑low heat, adjusting the heat and deglazing with a splash of liquid if the pan starts to scorch.
- Cut onions evenly. Slice pole‑to‑pole into uniform half‑moons so they cook at the same rate and don’t burn in patches while others stay pale.
- Use good stock. The broth should be flavorful on its own; a mix of beef and chicken stock or a rich homemade/“better than bouillon” style concentrate gives the best depth.
- Choose melt‑friendly cheese. Young Gruyère is classic because it melts smoothly and adds nutty, savory flavor; you can blend in a little low‑moisture mozzarella for extra stretch if you like.
- Toast the bread until dry. Baguette slices should be lightly golden and crisp before they go on the soup so they hold their structure under the cheese instead of turning soggy.
- Broil with a tray. Always set bowls on a rimmed baking sheet under the broiler so they’re easy to move and any bubbling cheese drips stay contained.
- Make it ahead. The soup (without bread and cheese) actually tastes better the next day; cool and refrigerate up to 3–5 days or freeze up to about 3 months, then reheat and top with fresh cheese toasts.
FAQs
Q: Can I make French onion soup in advance?
A: Yes. Cook the soup completely, cool, and refrigerate for 3–5 days, or freeze in airtight containers for up to 3 months. Reheat on the stove, then add toasted bread and broiled cheese just before serving so the texture stays perfect.
Q: What if I don’t have Gruyère?
A: Gruyère is traditional for its nutty flavor and excellent melt, but other Alpine‑style cheeses like Emmental, Comté, or Swiss can work, and some cooks blend in low‑moisture mozzarella for extra stretch while keeping most of the flavor from Gruyère or a similar cheese.
Q: How dark should the onions be?
A: Aim for a rich golden‑brown color—deeper than “soft and yellow,” but not black or bitter. If they’re browning too fast, lower the heat and add a teaspoon or two of water or stock to loosen the fond and keep them from scorching.
Q: Can I make this vegetarian?
A: Yes. Swap the beef stock for a very robust vegetable stock (or a mix of veggie stock and a splash of soy sauce or miso for savoriness) and keep the rest of the method the same; just note the flavor will be lighter than the classic beef‑based version.
Q: Why is my soup too salty or too bland?
A: Stocks vary in salt; start with less salt at the onion stage and adjust only after the soup has simmered. If it’s too salty, add a bit of unsalted stock or water to dilute, then rebalance with a splash of wine or a tiny pinch of sugar if needed.
