French Onion Soup, Portuguese-Style

This French onion soup borrows a couple of flavors from Portugal: dry Portuguese white wine in the broth and, if you like, tangy São Jorge cheese under the toast. Slowly browned onions, savory beef broth, and crisp bread still make it recognizably French onion soup; the Portuguese touches are an optional, flavorful variation rather than a claim that this is a traditional Portuguese dish.

Ingredients

3 lb yellow onions (about 6 medium onions; 1.36 kg), peeled and thinly sliced
4 tbsp unsalted butter (57 g)
1 tbsp olive oil (15 ml)
1 tsp fine salt (5 g), plus more to taste
2 garlic cloves (about 6 g), finely chopped
1 tbsp all-purpose flour (8 g), optional, for a slightly fuller broth
1 cup dry Portuguese white wine (240 ml), or another dry white wine
8 cups beef broth (1.9 L), preferably low-sodium so you can season the finished soup
4 fresh thyme sprigs (about 2 g), or 1 tsp dried thyme (1 g)
1 bay leaf (about 0.2 g)
1 tbsp Worcestershire sauce (15 ml), optional
¼ tsp freshly ground black pepper (about 0.5 g)
12 baguette slices, about ½ in (1.25 cm) thick (roughly 180 g total)
2 cups grated Gruyère or São Jorge cheese (about 200 g); São Jorge is a firm, flavorful Azorean cheese, while Gruyère gives the more familiar French-style topping
1 tsp sherry vinegar (5 ml), optional, to brighten the broth at the end

Instructions

Prepare the ingredients. Peel and slice the onions evenly, about ⅛ in (3 mm) thick; even slices cook at a similar rate. Chop the garlic, grate the cheese, and slice the baguette if it is not already cut. Set out six oven-safe soup bowls if you plan to melt the cheese under the broiler. This preparation takes about 20 minutes.
Start the onions slowly. Set a large, heavy pot or Dutch oven over medium heat. Add the butter, olive oil, sliced onions, and salt. Stir to coat the onions, then cook for 10 minutes, stirring every few minutes, until they soften and release liquid. If they begin browning in patches before softening, reduce the heat to medium-low.
Caramelize until deep gold. Continue cooking for 35 minutes, stirring every 3 to 5 minutes and scraping the pot as needed. Near the end, stir more often because the sugars can catch on the bottom. The onions should become very soft and a deep amber brown, reduced to a small fraction of their original volume. If the pot looks dry or the onions stick, add a tablespoon of water and scrape up the browned bits; do not rush this stage over high heat.
Add garlic, flour, and wine. Stir in the garlic and cook for 30 seconds. If using flour, sprinkle it over the onions and stir for 1 minute so no dry pockets remain. Pour in the wine, scraping the bottom of the pot to release browned flavor, and simmer for 2 minutes. The wine should lose its sharp raw smell, but it does not need to disappear completely.
Simmer the soup. Add the beef broth, thyme, bay leaf, Worcestershire sauce if using, and black pepper. Bring the soup to a gentle simmer, then lower the heat and cook uncovered for 25 minutes. Keep it at a quiet bubble rather than a vigorous boil. Remove the thyme stems and bay leaf, taste, and add salt as needed. Stir in the optional sherry vinegar if the broth tastes rich but a little flat.
Toast the bread. While the soup simmers, heat the oven to 425°F (220°C). Arrange the baguette slices in one layer on a baking sheet and toast for 5 minutes, until dry and lightly golden. The slices should be firm enough to support the cheese but need not be browned all the way through. Remove them from the oven and switch the oven to broil.
Top and broil. Ladle the hot soup into six broiler-safe bowls placed on a sturdy baking sheet. Float two baguette slices on each bowl and divide the grated cheese over the bread, letting a little fall onto the soup’s surface. Broil for about 3 minutes, watching closely, until the cheese is bubbling and browned in spots. Broilers vary, so take the tray out as soon as the topping is melted and golden. If your bowls are not broiler-safe, broil the cheese-topped toast on the baking sheet and place one piece on each bowl just before serving.
Serve carefully. Let the bowls stand for 2 minutes before carrying them to the table; the soup and ceramic will be extremely hot. Set each bowl on a heatproof plate and warn diners that the cheese-covered toast can hold heat.

Tips

Give the onions time. Their slow browning builds the soup’s defining sweetness and savory depth. Keep the heat moderate and stir more frequently as they darken. A little water loosens stuck-on browned bits; a burnt, black layer will make the broth bitter, so lower the heat if it develops.
Choose wine for flavor, not sweetness. A dry Portuguese white wine fits the variation, but any dry white wine works. Avoid sweet wine, which can make the broth taste cloying. For an alcohol-free version, use extra broth and add a teaspoon of sherry vinegar or lemon juice near the end for brightness.
Season after the broth simmers. Broth, Worcestershire, and cheese all contain salt, and their levels vary. Starting with a restrained amount of salt and tasting before serving prevents an overly salty soup.
Use a good melting cheese. Gruyère melts smoothly and has a nutty taste; São Jorge brings a sharper, more assertive Portuguese accent. If neither is available, use Emmental or a mix of Swiss-style cheese and a little Parmesan. A very dry or low-fat cheese may melt less smoothly.

Serving Suggestions

Serve the soup as a first course or make it the centerpiece of a simple winter meal. A green salad with a sharp vinaigrette balances the rich broth and melted cheese, while roasted vegetables or a plate of sliced pears make easy accompaniments. Because each bowl already includes bread and cheese, keep additional sides light. If serving guests, bring the bowls straight from the broiler on heatproof plates and provide a spoon along with a fork for the softened toast.

For a less rich serving, ladle the soup into bowls and offer the cheese toast on the side rather than covering each portion. This also makes it easier to control the amount of bread and cheese. A little chopped parsley can add color, though it is not essential to the flavor.

Variations

Make it without wine: Replace the wine with an equal amount of beef broth. Add the optional vinegar only after simmering, tasting a little at a time so it brightens rather than makes the soup sour. This keeps the soup savory without trying to imitate wine’s exact flavor.

Use vegetable broth: For a meat-free version, replace the beef broth with a robust vegetable broth and check that the Worcestershire sauce is vegetarian, or leave it out. The result will be lighter and less beefy, but deeply browned onions still give it plenty of character. Choose a low-sodium broth and adjust the salt at the end.

Try another cheese: São Jorge is a distinctive choice when you want a Portuguese note, but it can be harder to find outside Portugal. Gruyère is a dependable alternative; Emmental, Comté, or a mild Swiss cheese also melt well. Use a cheese you enjoy on its own, since its flavor is concentrated by the bubbling topping.

Make it gluten-free: Omit the flour, which is optional, and use gluten-free bread for the topping. Check the labels on broth and Worcestershire sauce as well. The soup will be a little less thick, but it will still have body from the soft onions.

Storage and Reheating

For the best texture, store the soup and toasted bread separately. Transfer leftover soup to shallow, covered containers and refrigerate it within 2 hours of cooking; it keeps for 3 to 4 days. Do not store assembled bowls with bread and cheese, since the toast quickly becomes soggy. Keep any extra toasted slices in an airtight container at room temperature for a day, though freshly toasted bread is best.

Reheat only the amount you plan to eat in a saucepan over medium-low heat, stirring occasionally until steaming throughout. For food safety, USDA FSIS recommends reheating leftovers to 165°F (74°C); check the soup with a food thermometer. Add a splash of broth or water if it has thickened in the refrigerator. Toast fresh bread, add cheese, and broil just before serving.

To freeze, cool the soup promptly in shallow containers and freeze it without the bread or cheese for up to 2 to 3 months for good quality. Thaw it in the refrigerator, then reheat to 165°F (74°C). The onions may soften further after freezing, but the flavor remains useful for a quick meal. Avoid repeatedly cooling and reheating the same large pot; portioning makes it easier to warm only what you need.

Frequently Asked Questions

Can I make French onion soup ahead of time?

Yes. Cook the soup through the simmering step, cool and refrigerate it, then reheat it the day you plan to serve. Toast the bread and add the cheese only at the end. The soup’s flavor often settles and melds during storage, while separate toppings keep their crispness.

Why are my onions not turning brown?

They may be releasing water faster than it can evaporate, or the pan may be crowded and the heat too low. Keep cooking uncovered so moisture can escape, and stir regularly. If the pot is very full, use a wide heavy pot; avoid turning the heat up sharply, which can scorch the onions before they caramelize evenly.

Do I have to use oven-safe bowls?

No. Broiler-safe bowls create the classic melted cheese cap, but they are not necessary. Toast baguette slices, add cheese, and broil them on a baking sheet; then float a finished cheese toast on each bowl of hot soup. Never put an ordinary bowl under a broiler.

What can I use instead of beef broth?

Choose a rich vegetable broth for a meat-free soup, or use chicken broth for a lighter flavor. Either will change the traditional beefy character, so taste carefully and adjust the salt and black pepper after simmering. Low-sodium broth gives you more control.

Can I skip the flour?

Yes. Flour is optional and only gives the broth a little extra body; it is not required for caramelizing onions or making the soup. Leave it out for a thinner, clearer broth, or use a suitable gluten-free flour if you want some thickening.

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Safety notes: safe minimum internal temperatures from USDA FSIS; raw and undercooked fish guidance from the U.S. FDA. Food safety notes

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