Quick Answer
To make French onion soup, slice about 3 pounds of yellow onions and cook them slowly in butter for 45 to 60 minutes until deep golden brown.
Deglaze the pot with a splash of dry white wine or sherry, add about 6 cups of beef broth and a little thyme, and simmer for 20 to 30 minutes.
Ladle it into oven safe bowls, top with toasted baguette and plenty of Gruyere, and broil until bubbly and browned.
Why Does French Onion Soup Take So Long?
The flavor comes almost entirely from caramelized onions. Slow cooking turns their natural sugars a rich brown and creates a sweet, savory depth.
Rushing with high heat burns the outside before the inside softens, leaving bitter onions. Low and slow is the whole secret, so plan about 1 1/2 hours start to finish.
What Do You Need?
- 3 pounds yellow onions (about 5 large), halved and thinly sliced
- 4 tablespoons butter, plus a splash of olive oil
- 1 teaspoon salt and 1/2 teaspoon sugar (optional)
- 1/2 cup dry white wine or dry sherry
- 6 cups beef broth (or half beef, half chicken)
- 2 sprigs fresh thyme and 1 bay leaf
- 1 tablespoon flour (optional, for body)
- 1 baguette, sliced and toasted
- 6 ounces Gruyere, grated, plus a little Parmesan
Yellow onions are the classic choice. Sweet onions caramelize faster but can taste a little flat, so I like a mix.
How Do You Make French Onion Soup, Step by Step?
1. Slice evenly. Cut the onions pole to pole into thin half moons so they cook at the same rate.
2. Start them. Melt the butter with the oil in a heavy Dutch oven over medium heat. Add the onions and salt, and stir to coat.
3. Sweat. Cover for about 15 minutes so they soften and release their juices.
4. Caramelize. Uncover, lower to medium low, and cook for 30 to 45 more minutes, stirring every few minutes. Scrape up the brown bits from the bottom each time.
5. Fix sticking. If the bottom starts to darken too fast, add a tablespoon of water and scrape. This deglazes the fond into the onions.
6. Add flour. Once the onions are deep amber, sprinkle in the flour and stir for 1 minute.
7. Deglaze. Pour in the wine or sherry and scrape the pot clean. Let it bubble for 2 minutes.
8. Simmer. Add the broth, thyme and bay leaf. Simmer gently for 20 to 30 minutes, then season with salt and pepper.
9. Broil. Ladle into oven safe crocks on a sheet pan. Float a slice or two of toast on each, pile on the cheese and broil for 2 to 4 minutes until bubbling and spotted brown.
What Is the Best Cheese for French Onion Soup?
Gruyere is the classic. It melts smoothly, browns well and has a nutty flavor that suits the sweet onions.
Comte, Emmental, Swiss or a little fontina also work. A light dusting of Parmesan adds a salty crust.
Can You Make French Onion Soup Without Wine?
Yes. Deglaze with extra broth plus 1 teaspoon of sherry vinegar or balsamic vinegar for brightness.
A splash of Worcestershire sauce or a bit of soy sauce adds savory depth when you skip the wine.
Can You Make It Vegetarian?
Swap the beef broth for a rich mushroom or vegetable broth. A tablespoon of soy sauce and a few dried porcini help mimic the depth of beef stock.
Check that your cheese is made with vegetarian rennet if that matters to you.
How Do You Store and Freeze French Onion Soup?
Refrigerate the soup, without bread or cheese, in a covered container for 3 to 4 days. It tastes even better on day two.
The soup base freezes well. The National Center for Home Food Preservation suggests cooling soups quickly and freezing them in rigid containers with headspace. Add the toast and cheese only when you reheat and broil.
How Should You Store Onions for Soup?
Michigan State University Extension recommends storing whole dry onions in a cool, dry, dark, well ventilated place, and not in plastic bags.
Keep onions away from potatoes. Once cut, wrap leftovers and refrigerate them.
What Mistakes Ruin French Onion Soup?
- Too much heat: burnt onions taste bitter and the soup never recovers.
- A crowded small pan: onions steam instead of browning. Use a wide Dutch oven.
- Weak broth: the broth is half the flavor, so use the best you can find or make your own.
- Soggy bread: toast the baguette slices until dry and crisp before topping the soup.
- Not enough cheese: cover the toast edge to edge so it melts over the rim.
What Should You Serve With French Onion Soup?
A crisp green salad with a sharp vinaigrette balances the richness. Roast chicken or a simple steak turns it into a full dinner.
For drinks, a dry white wine or a light red such as Pinot Noir pairs well with the sweet onions and nutty cheese.
How Do You Make Homemade Croutons for the Topping?
Slice a day old baguette into 1/2 inch rounds, brush both sides lightly with olive oil or melted butter and bake at 375 F for about 10 to 12 minutes until crisp and golden.
Rub each warm slice with a cut garlic clove for extra flavor. Dry, sturdy toast holds up under the cheese without turning to mush.
Frequently Asked Questions
Can I caramelize onions in a slow cooker?
Yes. Cook sliced onions with butter on low for about 10 hours, then finish on the stove.
Why are my onions not browning?
The pot may be crowded or the heat too low. Give them time and a wide pan.
What bowls do I need?
Oven safe ceramic crocks that can handle the broiler.
Can I make it ahead for a party?
Yes. Make the soup a day early and broil just before serving.
The Bottom Line
French onion soup is simple ingredients plus patience. Caramelize the onions slowly until deep brown, deglaze, simmer with good broth, and finish under the broiler with bread and Gruyere.
Make a big pot on a cool weekend and freeze the extra. A bowl of it on a weeknight feels like a bistro dinner.
