Crusty French bread topped with melted cheese and sitting in a sweet onion broth…this French Onion Soup Casserole is a must-serve side dish or easy vegetarian dinner for all of your cozy gatherings this season!
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 roasted turkey, grilled steak, pot roast, fresh seafood, or baked chicken. It pairs beautifully with just about any main course, it’s easier to prepare than individual bowls of soup, and the rich broth base cannot be beat!
If you want to make this dinner a true one-dish meal, you can add cooked chicken, sausage, or ground beef into the soup base when you transfer the mixture to the baking pan. It’s also a lovely vegetarian main course option with a salad alongside for some leafy green freshness!
While the cook time is longer than my normal quick-prep recipe, it’s super easy and it only requires about 10 minutes of actual hands-on time. I like to prep the French Onion Soup base for the casserole in advance (up to a day or two ahead of time), so that when I need to pop it in the oven on a busy weeknight everything is ready to go!
I hope that you enjoy this versatile, cozy, and incredibly rich dish just as much as my family does!
French Onion Soup Casserole
- 3 medium sweet onions sliced
- 3 tablespoons butter
- 4 cups beef broth
- 1 teaspoon Worcestershire sauce
- Approximately 4 ounces French baguette bread sliced about ½-inch in thickness (approximately 10-12 small slices)
- 1 cup 4 ounces shredded mozzarella cheese
- ¼ cup grated Parmesan cheese
- Melt butter in a large saucepan over low heat.
- Add onions and cover. Cook for about 30 minutes, stirring occasionally.
- Add the beef broth and the Worcestershire sauce. Heat the broth mixture until it boils.
- Reduce heat to low. Allow to simmer, uncovered, for about 30 minutes. The broth will reduce.
- Pour onion and broth mixture into a medium greased casserole dish (you can use a 1 ½-quart baking dish, an 11x7-inch baking dish, a 9-inch square baking dish, or something similar in size).
- Lightly toast the slices of bread.
- Place toasted bread in a single layer on top of onion/broth mixture.
- Cover bread with a thick layer of the shredded mozzarella and top with grated Parmesan.
- Bake, uncovered, in a 350 degree oven for 20-30 minutes, or until cheese is melted and brown on top.
Want to Prep Ahead? Prepare the French Onion Soup base for the casserole (through Step 5) up to a day or two in advance. Keep it covered in the refrigerator until you’re ready to bake it. Before baking, allow the dish to sit on the counter for about 30 minutes so that it has time to come to room temp before you put it in the oven.
I also like to toast the bread in advance. Allow the toast to cool completely and then just store it in a zip-top bag on the counter until you’re ready to bake the casserole. While the oven preheats, you can add the toast and cheese to the top of the dish and then just pop it in the oven. No last-minute scurrying around the kitchen!