Everything you love about French onion soup is baked together in a scrumptious casserole. A wonderful side dish for any seasonal meal.
If you love French onion soup - especially the cheesy toasted bread on top - you will love this casserole. It's loaded with chewy sourdough, caramelized onions, and plenty of melty cheese.
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Why you will love this casserole recipe
- Comfort food - This casserole tastes like a warm hug!
- Irresistible flavor - The combination of tangy sourdough, sweet caramelized onions, and nutty Gruyere is a match made in heaven.
- Versatile side dish - Serve with steak, pork tenderloin, chicken, or turkey.
- Make-ahead - Save time by preparing the individual components 2-3 days ahead of time. Simply toss together the ingredients when ready to bake.
For more French onion soup inspiration, try French Onion Chicken Skillet - pan-seared chicken topped with sweet caramelized onions and nutty Gruyere cheese.
Ingredient notes
- Sourdough bread - I love the tangy flavor and chewy texture of sourdough. French bread or Ciabatta can also be used.
- Onions - I always reach for the yellow variety (such as Vidalia) when caramelizing onions, but white or red onions can also be used.
- Gruyere cheese is my favorite for its nutty flavor and good melting quality. Provolone and Fontina are also good options.
- Beef broth adds a rich, traditional flavor. Chicken broth can also be used.
- Thyme is a classic favor here. Fresh is preferred, but dried can certainly be used. For dried, use ⅓ the amount of fresh called for in the recipe.
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Step-by-step instructions
Please see the recipe card for the complete instructions and ingredient amounts.
- Melt butter over medium heat and add the onions. Stir to coat and cook, stirring occasionally, until softened, 8-10 minutes.
- Meanwhile, preheat the oven to 350 degrees and spread bread cubes on a sheet pan. Bake for 10-15 minutes until dry and slightly crispy.
- When the onions have softened, add thyme and season with salt and pepper.
- Continue cooking and stirring occasionally until the onions have turned golden brown. This will take 30-40 minutes. If the onions start to dry out, add 1-2 tablespoons of water or beef broth as needed.
- Stir in Worcestershire sauce and vinegar. Taste and adjust salt and pepper as needed.
- Stir in toasted bread cubes. Add the beef broth and toss to combine. The bread should be moist but not soupy. Add more broth if necessary.
- Stir in half of the cheese. Top the casserole with the remaining cheese.
- Bake at 375 degrees for 20-25 minutes until the cheese is golden brown and melted. Serve.
Expert Tips
- Use freshly shredded cheese for the best flavor and melting quality.
- Don't rush the onions. Be patient. It takes time to develop the sweet caramelization.
- Make extra caramelized onions to use in caramelized onion dip or on caramelized onion, fig, and blue cheese flatbread.
- Use beef broth for added flavor and richness. I prefer the low-sodium variety so that I can control the amount of salt.
- Use an oven-safe skillet to save on dishes. I love using a braiser with handles for stove-to-oven dishes. A baking dish can also be used.
Recipe FAQs
French onion soup is traditionally made with yellow onions and beef broth, while onion soup can include a variety of onions and broths.
French onion soup pairs well with grilled sandwiches, steak or chicken dishes, fish, and roasted vegetables. Try serving with steak and white cheddar panini or Italian chicken cutlets.
For a delicious twist, stir in caramelized mushrooms. You can turn this easy casserole into a one-dish meal by adding cooked chicken, sausage, or bacon.
The caramelized onions can be made 2-3 days in advance and stored in the refrigerator. You can also toast the bread cubes 2-3 days in advance and store them in an airtight container at room temperature. Combine the ingredients when ready to bake.
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📖 Recipe Card
French Onion Soup Casserole
Ingredients
- 1 loaf sourdough bread (approx. 14 ounces)
- 4 cups sliced yellow onions (such as Vidalia)
- 3 tablespoons butter
- 1 tablespoon fresh thyme (or 1 teaspoon dried)
- salt and pepper
- 1 teaspoon Worcestershire sauce
- 1 teaspoon white wine vinegar
- ¾ cup low-sodium beef broth (plus more as needed)
- 8 ounces Gruyere cheese (shredded)
Instructions
- Preheat the oven to 350℉.
- In a large shallow oven-safe skillet over medium heat, melt the butter. Add the onions and toss to coat. Cook, stirring occasionally, until softened, 8-10 minutes.
- Meanwhile, cut the bread into 1-inch cubes. Spread on a half-sheet pan and bake for 10-15 minutes until dry and slightly crisp. Set aside. Turn the oven up to 375℉.
- When the onions are soft, add the thyme and season with salt and pepper. Continue cooking, stirring occasionally, until golden brown, 30-40 minutes. If the onions dry out, add 1-2 tablespoons of water as needed.
- Stir in Worcestershire sauce and vinegar. Taste and season with salt and pepper as needed. Stir in bread and toss together.
- Add the beef broth and stir to combine. The bread should be moist but not soupy. Add more broth if needed.
- Add half of Gruyere cheese and fold together. Top with the remaining cheese.
- Bake at 375℉ for 20-25 minutes until golden brown on top. Serve.
Notes
- Use freshly shredded cheese for the best flavor and melting quality.
- Don't rush the onions. It takes time - and a little patience - to develop the sweet caramelization.
- To make ahead: caramelize the onions up to 2-3 days in advance and store in the refrigerator. Toast the bread cubes up to 2-3 days in advance and store them in an airtight container. Combine the ingredients and bake according to the directions.
- Make extra caramelized onions to use in caramelized onion dip or on pizza like this fig, blue cheese, and caramelized onion flatbread.
Nutrition
Nutritional information is an estimate and will vary depending on the exact amounts and specific ingredients used.
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