Gratinée onion soup is a great classic of French cuisine: slowly browned onions, a fragrant broth, and a slice of bread covered with melted, bubbly cheese. To make this recipe for 6 people a success, take the time to color the onions without burning them, then gratinate each bowl just before serving. Here you will find the ingredients, detailed steps, solutions for caramelization issues, alcohol-free variations, and storage tips. Recommended equipment is grouped at the end of the recipe. Preparation Estimated cooking time Total estimated time Servings Difficulty 20 min Approx. 1 hr 10 min Approx. 1 hr 30 min 6 people ★★☆☆☆ Easy The time may vary depending on the size of the pot, the thickness of the onion strips, and the water content of the onions. Rely primarily on their color and texture. 🛒 Gratinée onion soup ingredients for 6 people The soup 1 kg yellow onions 50 g butter 2 tablespoons olive oil 1.5 liters beef or vegetable broth 20 cl dry white wine 1 tablespoon flour 1 bay leaf 1 sprig of thyme Salt, pepper The bread and cheese for the topping 6 large slices of traditional baguette 250 g grated Gruyère or Comté cheese 1 garlic clove 👨🍳 CuisinerTelUnChef Chef's Tip Yellow onions are well-suited for this long cooking process. Mix Comté and Gruyère to vary the flavors. Choose a low-sodium broth: the reduction and the cheese already intensify the seasoning. A slightly stale, well-toasted baguette holds up better in the broth. 🔪 Necessary utensils Chef's knife or mandoline with a food guard — for uniform slicing Stable cutting board Large heavy-bottomed Dutch oven or pot Wooden spoon or spatula Cheese grater 6 oven- and broiler-safe bowls Baking sheet to move the bowls more easily 👨🍳 How to prepare gratinée onion soup? Step 1 — Peel and slice the onions Peel the onions and cut them into thin, uniform strips. Consistent thickness makes cooking easier. If using a mandoline, always use the safety pusher and stop slicing when the piece becomes too small. Our guide to slicing an onion details the preparation techniques. Step 2 — Melt and then brown the onions Melt the butter with the olive oil in a large pot. To choose a suitable cooking fat, check out our guide to culinary oils. Add the onions and a small pinch of salt. Let them melt first, then cook over low to medium-low heat, stirring regularly. Allow about 35 to 40 minutes, sometimes longer, to achieve soft, golden-brown onions. They must lose their water and brown gradually. Do not cover during the coloring phase: moisture must be able to evaporate. 👨🍳 CuisinerTelUnChef Chef's Tip Pale onions swimming in their own juices often lack sufficient time, cooking surface area, or heat. Use a wide pot and gently adjust the heat. If they stick and brown too quickly, lower the heat and add a tablespoon of water to scrape up the fond. Black coloring and a bitter smell indicate they are burning. Step 3 — Deglaze and simmer Sprinkle the flour over the golden onions. Stir and cook for about a minute, without letting the flour burn. Pour in the white wine, scraping the bottom of the pot, then let it reduce for a few minutes. Gradually add the broth, thyme, and bay leaf. Bring to a simmer and let cook for 25 minutes on low heat. Remove the aromatics. Taste before seasoning with salt and pepper to your liking. Our guide to aromatic herbs will help you dose these flavors without masking the onion. Step 4 — Toast the bread and rub with garlic Toast the baguette slices on both sides in the oven or toaster. They should be dry on the surface and lightly golden, not burnt. Rub them with the garlic clove cut in half. 👨🍳 CuisinerTelUnChef Chef's Tip Prepare the soup in advance, but keep the toasted bread and cheese separate. Assembling at the last minute preserves the contrast between the broth and the gratinated crust. To organize your preparation, see our batch cooking guide. Step 5 — Assemble the bowls and gratinate Preheat the oven broiler. Place the broiler-safe bowls on a stable tray. Pour in the piping hot soup, place the bread slices on top, and cover with grated cheese, about 40 g per bowl. Place under the broiler for about 5 to 7 minutes, watching continuously: the duration depends on the power of the broiler and the distance from the heating element. Remove the bowls when the cheese is melted and golden. Do not use the broiler to reheat cold soup throughout. Serve with caution: the bowls and broth will remain very hot. Avoid thermal shock and follow the manufacturer's instructions for your bowls. ⭐ The secrets of a successful onion soup True coloring: the onions must be golden and soft before adding the broth. A tasty but low-salt broth: it complements the onion without overpowering the cheese. Well-toasted bread: it holds up better on the surface of the soup. Freshly grated cheese: spread it evenly for a uniform gratin. Last-minute assembly: do not let the bread soak for long before broiling. Broiler monitoring: just a few seconds can be the difference between a golden crust and burnt cheese. 🔄 Onion soup variations With Port Add a splash of Port during the deglazing for a rounder note. Reduce it before adding the broth. Vegetarian version Use vegetable broth. For a strictly vegetarian version, also check the cheese's rennet: some cheeses use animal rennet. Without wine Replace the 20 cl of white wine with additional broth. If you want a touch of acidity, add a few drops of cider vinegar at the end and taste before adding more. With blue cheese Replace part of the Comté or Gruyère with a few pieces of Bleu d'Auvergne. Taste the soup before salting: blue cheese can be quite salty. Forest style Sauté mushrooms separately to evaporate their water, then add them to the soup. Check our mushroom guide for preparation tips. With dry cider Replace the white wine with the same amount of dry cider. This variation adds a fruity note; keep in mind that cider remains an alcoholic beverage. Without flour Flour provides a slight thickening agent, but you can omit it for a thinner soup. For a gluten-free version, also choose appropriate bread and broth. ❌ Mistakes to avoid Burning the onions: lower the heat as soon as browning accelerates too much. Adding broth before browning the onions: once submerged, they will not develop the same color. Crowding onions into a small pan: their water evaporates less easily. Over-salting at the start: the broth reduces and the cheese adds salt. Using soft bread: toast it before assembly. Broiling cold soup: heat the soup on the stove first. Using bowls that aren't broiler-safe: not all ceramic containers are suitable. Leaving the oven while broiling: keep an eye on the coloring. 🥗 What to serve with gratinée onion soup? The bread and cheese make this a hearty soup. For a light meal, serve with a green salad or a lamb's lettuce salad with walnuts. A charcuterie board or a slice of quiche lorraine fits a heartier bistro menu. To vary seasonal meals, discover our autumn vegetable guide. 🌡️ Storage, freezing, and reheating In the refrigerator Store the soup alone, without bread or cheese, in sealed containers in the refrigerator at a maximum of 4°C, for up to three days. Divide large quantities into multiple shallow containers and refrigerate within two hours of preparation; do not let the pot sit out overnight at room temperature. In the freezer Freeze the soup alone in portions for up to three months to maintain quality. Date the containers and leave space for expansion. Thaw in the refrigerator before reheating. Reheat then gratinate Reheat in a saucepan until the soup is piping hot throughout, stirring occasionally. Add a little broth or water if it has thickened too much. Then assemble the bowls with freshly toasted bread and the cheese. Only reheat the portions you intend to serve. 🥗 Estimated nutritional values per serving The values below are approximate estimates for one serving including bread and cheese. They vary depending on the broth, cheese, weight of bread slices, and the amount actually served; they do not constitute a formal nutritional analysis of the recipe. Nutrient Estimated quantity Calories ≈ 420 kcal Protein ≈ 18 g Fat ≈ 20 g Carbohydrates ≈ 38 g Fiber ≈ 4 g The recipe contains dairy, wheat, and possibly other allergens depending on the broth and cheese used. Check labels if you are cooking for someone with allergies. ❓ Frequently asked questions about onion soup Which cheese should I choose for the gratin? Comté and Gruyère melt well and add flavor. Mix them if you prefer a more complex crust. Grate the cheese and spread it over the entire surface of the bread. Can I prepare the soup the day before? Yes. Prepare and store only the soup in the refrigerator. Reheat in a saucepan, then add the bread and cheese when ready to gratinate. Why do the onions stay pale? They may need more time or remain too damp in a container that is too narrow. Let their water evaporate uncovered, use a wide pot, and gradually adjust the heat without burning them. Do I need to add sugar to caramelize? It is not necessary in this recipe. The onions develop their natural sweetness during cooking. Added sugar can also accelerate browning and make heat control more difficult. How can I replace the white wine? Use 20 cl of additional broth and, if desired, a few drops of cider vinegar at the end of cooking. Dry cider is another variation, but not an alcohol-free option. How do I prevent the bread from disintegrating? Choose a slice that is thick enough and well-toasted. Place it on the hot soup just before broiling, without letting it soak for too long. What if the soup is too thick or too salty? Dilute gradually with a little water or unsalted broth, then taste. If too thin, let it reduce gently before assembly, monitoring the seasoning. Can I gratinate the whole soup in one large dish? Yes, in a broiler-safe container. Heat the soup first, then add bread and cheese. Service will be less clean than with individual bowls; keep an eye on the coloring and handle the hot dish carefully. 🔗 To continue cooking French classics Pumpkin soup — another seasonal soup French cuisine guide — traditions and techniques for major classics 🛒 CuisinerTelUnChef utensils to master your onion soup Our chef's knives — for slicing onions Our mandolines — for uniform slices, with the safety pusher Our cheese graters — for grating Comté and Gruyère Our cutting boards — for stable preparation Cook like a chef! Take the time to brown the onions, taste the broth, and gratinate at the last moment for a hearty, fragrant soup.