Crusty French bread topped with melted cheese and sitting in a sweet onion broth…this French onion casserole is a must-serve side dish or easy vegetarian dinner for all of your cozy gatherings this season!
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If you enjoy French onion recipes, be sure to try this French onion chicken bake, this French onion pasta bake with spinach and mushrooms, and this dump-and-bake French onion chicken, too!
I made this yesterday and loved it! It is delicious!
– Janine
Don’t you just love a good bowl of French onion soup? This casserole takes all of those delicious flavors and bakes them into an easy dish that can be served alongside your favorite Thanksgiving turkey, cast iron filet mignon, Dutch oven pot roast, fresh seafood, pineapple glazed ham, or roast chicken.
How to Make French Onion Soup Casserole
This easy French onion soup casserole is versatile, cozy, and incredibly rich. You’ll find detailed instructions in the recipe card below, but here’s the overview:
- Cook the onions in butter for about 30 minutes. I know this may seem like a long time, but this low-and-slow process caramelizes the onions, giving your casserole the beautifully rich, French onion soup flavor. Don’t rush this step!
- Add the beef broth and the Worcestershire sauce, and bring the liquid to a boil.
- Reduce the heat and simmer, uncovered, for about 30 minutes. The broth will reduce. Remember, we’re making a casserole instead of a soup! Taste and season with salt and black pepper at this point, if desired.
- Pour the onion and broth mixture into a greased pan.
- Lightly toast the slices of bread.
- Place the toasted bread in a single layer on top of onion and broth mixture.
- Cover the bread with a thick layer of the shredded mozzarella and top with grated Parmesan.
- Bake, uncovered, until the cheese is melted and brown on top, about 20-30 minutes.
Serving Suggestions
This French onion casserole works nicely as a side dish with just about any main course, and it’s easier to prepare than individual bowls of soup. Try it with Crock Pot turkey tenderloin, a ham steak with brown sugar glaze, dump-and-bake cranberry chicken, or grilled tenderloin. It’s also a lovely meatless weeknight dinner alongside a kale apple salad or a classic Caesar salad.
This recipe was exactly what I needed to use up an abundance of onions. I had all the ingredients on hand. Thank you so much for a delicious dinner that was fun to make and enjoy. This dish is sweet and rich with simple ingredients. It doesn’t need any additional seasonings. I followed it as written. Yum!
– Stacy
Did you make this recipe?
If you enjoyed this recipe, please leave a comment with a 5-star review at the bottom of the post. Thank you!
French Onion Casserole
Ingredients
- 3 medium sweet onions, sliced
- 3 tablespoons salted butter
- 4 cups beef broth (use vegetable broth or vegetable stock for a vegetarian dish)
- 1 teaspoon Worcestershire sauce
- 4 ounces French baguette bread, sliced about ½-inch in thickness (approximately 10-12 small slices)
- 1 cup (4 ounces) shredded mozzarella cheese (or sub with Gruyere or Fontina when available)
- ¼ cup grated Parmesan cheese
- Optional garnish: chopped fresh thyme or parsley
Instructions
- Preheat the oven to 350°F. Grease a medium casserole dish (approximately 2 quarts, or about 11 x 7-inches or 9-inches square). Set aside.
- Melt the butter in a large saucepan over low heat.
- Add the onions and cover. Cook for about 30 minutes, stirring occasionally.
- Add the beef broth and the Worcestershire sauce; bring to a boil.
- Reduce the heat to low. Allow the liquid to simmer, uncovered, for about 30 minutes so that the broth reduces.
- Pour the onion and broth mixture into the prepared baking dish.
- Lightly toast the slices of bread.
- Arrange the toasted bread in a single layer on top of onion and broth mixture.
- Cover the bread with a thick layer of shredded mozzarella. Sprinkle grated Parmesan over top.
- Bake, uncovered, for 20-30 minutes, or until cheese is melted and lightly browned on top. If you prefer a darker, crispier topping, you can place the dish under the broiler for the final 1-2 minutes (just keep a close eye on it so that it doesn't burn). Garnish with chopped fresh herbs, if desired.
Notes
Nutrition
French Onion Soup Casserole Recipe Variations
- No mozzarella? You can use another good melting cheese such as gruyère cheese or Fontina. Sharp white cheddar would also be great!
- Any white crusty bread would work well for the topping. Try a homemade baguette recipe or this no-knead Dutch oven bread when you have the time!
- Use beef broth or beef stock for the most authentic flavor.
- Add meat such as chicken, ground beef, or sausage for extra protein.
- To serve a larger group, double all of the ingredients and bake the casserole in a 9 x 13-inch dish.
More Vegetable Casserole Recipes
Easy Broccoli Casserole
30 minutes mins
Green Bean Casserole with Frozen Green Beans
40 minutes mins
Spinach Casserole
40 minutes mins
This recipe was originally published in September, 2014. It was updated in November, 2024.
I made this and put 8 burger patties (seared and partially cooked) in bottom and covered with onion mixture, cheeses, bread abd more cheese over the bread…so delicous! Planning to make again for pot luck church dinner .
We’re so glad you enjoyed it, Gail! Thank you for trying it out and taking the time to leave a review.
Do you serve in bowls? Plate? Is it soupy or…
It’s fairly soupy. So, bowls work well!