French Onion Soup Kit: Make a Rich, Cheesy Soup at Home

This French onion soup kit is a ready-to-cook bundle of sweet onions, savory broth, seasonings, bread, and cheese—not a shelf-stable packet. It makes a classic French bistro-style soup with deeply browned onions and a toasted Gruyère topping, and measuring everything first makes the long, gentle onion-cooking step easier to manage.

The recipe serves four as a generous starter or two to three as a main course. You can cook the kit right away, or prepare the onions ahead and finish the soup when you are ready to serve.

Ingredients

6 medium yellow onions, about 3 lb (1.4 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
1 tsp granulated sugar (4 g), optional, to help the onions brown evenly
2 garlic cloves (6 g), finely chopped
1 tbsp all-purpose flour (8 g)
½ cup dry white wine (120 ml), optional; use extra broth instead for an alcohol-free version
6 cups beef broth (1.4 L), preferably low-sodium; use vegetable broth for a vegetarian soup
1 tsp dried thyme (1 g), or 1 tbsp fresh thyme leaves (3 g)
1 bay leaf (about 0.2 g)
¼ tsp freshly ground black pepper (0.5 g), plus more to taste
1 tbsp Worcestershire sauce (15 ml); choose a vegetarian version if needed
8 baguette slices, about ½ inch (1.5 cm) thick and 8 oz (225 g) total
2 cups grated Gruyère cheese (200 g)
½ cup finely grated Parmesan cheese (45 g)

Instructions

Prepare the soup kit. Peel and slice the onions into even, thin half-moons; uniform slices soften at roughly the same pace. Chop the garlic, measure the broth and seasonings, and grate the cheeses. Keep the bread and cheese separate from the soup ingredients so they can be toasted and added at the end. Allow about 25 minutes for this prep.
Start the onions. Set a large, heavy-bottomed pot or Dutch oven over medium heat. Add the butter, olive oil, sliced onions, and salt. Stir to coat the onions, then cook uncovered for 10 minutes, stirring every few minutes, until they have softened and released liquid. A wide pot helps moisture evaporate; if your pot is narrow, expect the browning stage to take a little longer.
Caramelize slowly. Lower the heat to medium-low. Stir in the optional sugar, then cook the onions for about 35 minutes, stirring and scraping the bottom every 3 to 5 minutes. They should become very soft and turn a deep golden brown, with no black, scorched patches. If the bottom starts to catch before the onions are brown, reduce the heat and add 1 or 2 tablespoons of water to loosen the browned bits. The full onion-cooking time is about 45 minutes.
Add garlic and flour. Stir in the garlic and cook for 30 seconds, just until fragrant. Sprinkle the flour over the onions and stir for 1 minute so it loses its raw taste. The flour gives the broth a little body; do not add more than listed, or the soup can become pasty.
Deglaze and simmer. Pour in the wine, if using, and scrape the pot to release the caramelized residue. Simmer for 2 to 3 minutes, then add the broth, thyme, bay leaf, pepper, and Worcestershire sauce. Bring the soup to a gentle simmer, lower the heat, and cook uncovered for 20 minutes. Remove the bay leaf, taste, and adjust salt and pepper. If you used regular-sodium broth, taste before adding extra salt.
Toast the bread. While the soup simmers, heat the oven to 400°F (200°C). Arrange the baguette slices on a baking sheet and toast for about 5 minutes, turning once if needed, until dry and lightly golden. Toasting helps the bread hold its shape under the soup and cheese. Switch the oven to broil when the bread is ready.
Top and broil. Ladle the hot soup into four broiler-safe ovenproof bowls set on a sturdy baking sheet. Float two toasted bread slices on each bowl and divide the Gruyère and Parmesan over the bread, letting a little cheese fall at the edges. Broil 4 to 5 minutes, watching continuously, until the cheese is melted, bubbling, and browned in spots. Broilers vary, so remove the bowls as soon as the topping reaches that stage. Let the bowls stand for 2 minutes before serving; they will be extremely hot.

Tips

Give the onions time. Their deep flavor comes from slow browning, not high heat or a large dose of sugar. Stir regularly and turn the heat down if you see dark, bitter-looking spots. A few tablespoons of water can help lift fond from the pot without stopping the process.
Choose a suitable pot and bowls. A heavy pot distributes heat more evenly and is less likely to scorch the onions. Use bowls labeled oven-safe and broiler-safe; ordinary ceramic or glass bowls may crack under direct broiler heat. If you do not own suitable bowls, see the serving method below.
Make the kit vegetarian if needed. Use vegetable broth and vegetarian Worcestershire sauce, which avoids the anchovies found in many standard versions. The result is a little lighter and less savory than a beef-broth version; a small splash of soy sauce can add depth, but taste before salting.
Do not rush the topping. Broiled cheese can go from browned to burnt quickly. Keep the pan on a middle or upper rack where you can watch it, and use the oven light rather than walking away.

Serving Suggestions

Serve each bowl as soon as the cheese is bubbling, with a wide spoon and a sturdy knife for breaking through the bread cap. The soup is rich enough to work as a main course with a crisp green salad dressed in vinaigrette. For a lighter first course, serve smaller portions before roast chicken, a simple vegetable tart, or a meal built around roasted vegetables.

If you do not have broiler-safe soup bowls, ladle the soup into ordinary serving bowls and arrange the toasted bread on a baking sheet. Top the bread with the cheese and broil it separately until melted and browned, then place one or two cheese toasts on each bowl. This gives you the same contrast of savory broth and crisp, cheesy bread without putting unsuitable bowls under the broiler.

Variations

Alcohol-free: Leave out the wine and deglaze with ½ cup (120 ml) of broth. The soup will be slightly less bright, but the browned onions still give it plenty of flavor.
Vegetarian: Use a full-bodied vegetable broth and vegetarian Worcestershire sauce. A teaspoon of soy sauce or miso stirred into the broth can add savory depth; reduce added salt because both can be salty.
Different cheese: Comté or Emmental melts well in place of Gruyère. Swiss cheese is a practical substitute, though its flavor is milder. Keep a little Parmesan for a sharper, salty finish if available.
Gluten-free: Omit the flour or use 1 tbsp (8 g) gluten-free all-purpose flour. Choose gluten-free bread and check the broth and Worcestershire label. Without the flour, the broth will be thinner but still flavorful.
Thicker, onion-forward soup: Reduce the broth to 5 cups (1.2 L). For a looser, more broth-focused bowl, use 7 cups (1.65 L) and adjust seasoning after simmering.

Storage and Reheating

For the best texture, store the soup and toppings separately. Cool the soup promptly and refrigerate it within 2 hours of cooking, in a covered container. It keeps for 3 to 4 days in the refrigerator. Keep toasted bread in an airtight container at room temperature for a day; refrigerating bread makes it stale more quickly. Store grated cheese covered in the refrigerator and use it within a few days.

Reheat the soup gently in a saucepan over medium-low heat, stirring occasionally, until it is steaming throughout and reaches 165°F (74°C), the USDA FSIS safe temperature for reheated leftovers. Add a splash of broth or water if it has thickened. Toast fresh bread, top the hot soup, and broil just before serving; already-topped bowls do not reheat as evenly and the bread can turn soggy.

Freeze the soup base without bread or cheese for up to 2 to 3 months for best quality. Leave room in the freezer container for expansion, thaw overnight in the refrigerator, and reheat to 165°F (74°C). You can also freeze portions of the cooked onions, but keep the bread and cheese fresh for assembly. Do not leave soup at room temperature for more than 2 hours.

Frequently Asked Questions

Can I make the onions ahead?
Yes. Cool the caramelized onions and refrigerate them in a covered container for up to 3 to 4 days. When you are ready to cook, warm them in the pot, continue with the garlic and flour, and add the wine and broth. This shortens the day-of cooking considerably while preserving the slow-cooked flavor.

Why are my onions not turning brown?
They may still be releasing moisture, the pot may be crowded, or the heat may be too low. Keep cooking uncovered and stir periodically so moisture can evaporate. If the pot is narrow, divide the onions between two pans or allow extra time. Raising the heat sharply is not a good shortcut because the outside can burn before the onions soften.

Do I have to use sugar?
No. It is optional and does not replace the time needed to caramelize the onions. Yellow onions contain natural sugars and will brown with steady cooking. If you prefer a less sweet finish, simply leave the sugar out.

Can I prepare this French onion soup kit as a freezer meal?
Freeze the cooked soup base or the caramelized onions, not a fully assembled bowl with bread and cheese. Bread becomes soft after thawing, and cheese can separate or brown unevenly. Thaw the base in the refrigerator, reheat it to 165°F (74°C), then add freshly toasted bread and cheese for the best topping.

What broth gives the most traditional flavor?
Beef broth gives the soup a robust, savory character and is a common choice for French onion soup. A good vegetable broth makes a useful vegetarian alternative, while chicken broth produces a milder result. Choose low-sodium broth when possible so you can control the final seasoning.

Can I make the soup without ovenproof bowls?
Yes. Toast the baguette, top the slices with cheese, and broil them on a baking sheet until bubbling. Ladle soup into regular bowls and set the cheesy toasts on top at the table. The topping will not be fused to the rim, but the soup will still have crisp bread and melted cheese.

More recipes to cook

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

Spotted an error? Tell us and we will correct it (corrections policy).