Swiss onion soup is a savory, wine-scented soup of slowly browned onions and broth, finished with toasted bread and melted Gruyère. This version borrows the comforting baked-cheese finish familiar from several European onion soups, while keeping the broth and onion base straightforward; variations differ from kitchen to kitchen.
Ingredients
- 3 lb yellow onions (1.36 kg), peeled and thinly sliced
- 3 tbsp unsalted butter (42 g)
- 1 tbsp olive oil (15 ml)
- 1 tsp fine salt (6 g), plus more to taste
- 2 tbsp all-purpose flour (16 g)
- 1 cup dry white wine (240 ml)
- 8 cups beef broth (1.9 L), preferably lower-sodium, or vegetable broth
- 4 fresh thyme sprigs (about 2 g), or 1 tsp dried thyme (1 g)
- 1 bay leaf
- ¼ tsp freshly ground black pepper (about 0.5 g), plus more to taste
- 6 slices crusty bread, about ½ inch thick (180–240 g total)
- 1 garlic clove (3 g), peeled and cut in half
- 1½ cups grated Gruyère cheese (150 g)
Instructions
- Prepare the onions and oven. Peel the onions, cut them in half from root to tip, and slice them thinly. Grate the Gruyère and measure the remaining ingredients. Set a rack in the upper third of the oven and preheat it to 400°F (200°C); you will toast the bread while the soup simmers.
- Brown the onions slowly. Melt the butter with the olive oil in a large, heavy pot over medium heat. Add the onions and salt, then stir until they are coated. Cook for about 40 minutes, stirring every few minutes and more often near the end. The onions should become very soft, deeply golden, and reduced in volume. If browned bits begin sticking before the onions soften, lower the heat and add a tablespoon of water to loosen them. Avoid rushing this step: pale, barely softened onions make a thinner-tasting soup.
- Add flour and wine. Sprinkle the flour over the cooked onions and stir for 1 minute so it is no longer powdery. Pour in the white wine and scrape the bottom of the pot with a wooden spoon to release the browned bits. Let the wine bubble for 2 minutes, stirring, so its sharpest aroma cooks off.
- Simmer the soup. Add the broth, thyme, bay leaf, and black pepper. Bring the soup just to a boil, then reduce the heat to maintain a gentle simmer for 20 minutes. Stir occasionally. Remove the thyme stems and bay leaf, then taste and adjust the salt and pepper. Broths vary in saltiness, so make the final adjustment only after simmering.
- Toast the bread while the soup simmers. Arrange the bread slices on a baking sheet and bake at 400°F (200°C) for about 8 minutes, turning once, until dry and lightly crisp but not too dark. Rub one side of each warm slice with the cut side of the garlic clove. The toast should be sturdy enough to sit on the soup without immediately collapsing.
- Top and melt the cheese. Ladle the hot soup into six oven-safe bowls set on a sturdy baking sheet. Float a slice of toast on each bowl and divide the Gruyère evenly over the bread. Broil for 2–3 minutes, watching closely, until the cheese bubbles and develops golden spots. Broilers vary, so do not walk away. Use oven mitts to remove the tray and let the bowls stand for a few minutes before serving; they will be extremely hot.
Tips
- Give the onions time. Keep the heat at medium or lower and stir regularly. If the bottom of the pot is getting dark while the onions are still firm, lower the heat and loosen the fond with a small splash of water rather than letting it scorch.
- Choose a broth you like. Beef broth gives the soup a fuller, more traditional savory character, while vegetable broth keeps it meat-free and a little lighter. Lower-sodium broth makes it easier to control the finished seasoning.
- Use a suitable wine substitute. If you do not cook with wine, replace it with an equal amount of broth and add 1–2 teaspoons (5–10 ml) of white wine vinegar or lemon juice. The result will be less aromatic and less complex, so add the acid gradually and taste.
- Protect the bread from sogginess. Toast it until dry and crisp, and serve the soup as soon as the cheese melts. If you expect leftovers, store the soup and toast separately rather than keeping the bread in the broth.
Serving Suggestions
Serve each bowl as a generous first course or as a light main, with the cheese-topped bread in place. A crisp green salad with a mustard vinaigrette balances the soup’s buttery, savory richness. A plate of sliced apples, pears, or lightly dressed bitter greens also makes a simple accompaniment without competing with the cheese. If you are serving the soup as part of a larger meal, smaller bowls and one slice of toast per person are usually enough.
Keep extra grated Gruyère at the table for anyone who wants a little more, but taste before adding salt: the cheese and broth both contribute seasoning. Because the bowls come from the broiler very hot, set them on heatproof plates or trivets and let diners know before serving. If you do not have broiler-safe soup bowls, serve the hot soup in ordinary bowls and place the toasted, cheese-covered bread on top at the table.
Variations
Make it vegetarian: Use vegetable broth and check that it has a deep, savory flavor. Some vegetable broths are sweeter or milder than beef broth; a little extra thyme and freshly ground pepper can help, but adjust after tasting rather than adding more salt automatically.
Change the cheese: Gruyère melts smoothly and has a nutty, savory flavor. Emmental is a fitting Swiss-style alternative and tends to taste milder. Comté or a good-quality Swiss cheese can also work, though the exact flavor and browning will vary. Avoid relying on pre-shredded cheese if it is heavily coated in anti-caking starch, since it may not melt as evenly.
Make it without flour: Leave out the flour for a thinner, clearer broth and skip the step of stirring it into the onions. The soup will still taste rich from the browned onions, but it will have less body. For a heartier bowl, use an extra slice of toast instead of thickening the broth.
Serve it unbaked: Ladle the soup into bowls and offer toasted bread and grated cheese separately. This is useful when you do not have oven-safe bowls, and it lets everyone choose how much topping to add. The cheese will not form the same browned, bubbling cap, but the flavor remains satisfying.
Storage and Reheating
For best quality, store the soup without the bread or cheese topping. Refrigerate it within 2 hours of cooking in a covered, shallow container; it keeps for 3–4 days in the refrigerator. Let the soup cool enough to handle before refrigerating, but do not leave it on the counter to cool for an extended period. Keep toasted bread at room temperature in an airtight container for a day, or make fresh toast when serving.
Reheat only the portion you plan to eat in a saucepan over medium-low heat, stirring occasionally until steaming throughout. USDA FSIS guidance is to reheat leftovers to 165°F (74°C); check the center with a food thermometer. Add a splash of broth or water if the soup has thickened in the refrigerator. Put the hot soup in oven-safe bowls, add fresh toast and cheese, and broil briefly to finish. You can freeze the plain soup in a freezer-safe container for about 2–3 months for best quality; thaw it overnight in the refrigerator and reheat as above. Freeze without the toast and cheese, which are better added fresh.
Frequently Asked Questions
Is Swiss onion soup the same as French onion soup?
They share the key idea of slowly browned onions in broth, often served with bread and melted cheese, but recipes vary by region and household. This version uses Gruyère, a cheese associated with Switzerland, and dry white wine. It is best understood as a Swiss-inspired onion soup rather than a claim that there is one fixed recipe.
Can I make the soup ahead?
Yes. Make the onion-and-broth soup up to 3–4 days ahead and refrigerate it promptly in a covered container. Reheat it to 165°F (74°C), then add freshly toasted bread and cheese just before serving. Keeping the topping separate preserves the bread’s texture and gives you the best melted-cheese finish.
What onions work best?
Yellow onions are a dependable choice because they become sweet and savory as they cook, without making the finished soup taste overly sweet. White onions also work and may taste a little sharper. Red onions can be used, but they may give the broth a darker, less familiar color. Whatever type you choose, slice the onions evenly so they soften at roughly the same pace.
Why are my onions not browning?
A crowded pot, high heat, or onions releasing a lot of moisture can slow browning. Use a wide, heavy pot if possible, keep the heat moderate, and give the liquid time to evaporate before expecting the onions to color. Stir often enough to prevent scorching, but the onions do not need constant stirring. If your pot is small, cook in batches rather than piling in an unusually deep layer.
Can I use a different kind of bread?
Yes. A sturdy sourdough, country loaf, or baguette works well as long as the slices can support the cheese. Very soft sandwich bread tends to break down quickly in the soup. If using a narrow baguette, use enough slices to cover the surface of each serving and watch them closely as they toast, since thinner slices brown faster.
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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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