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+ servings
5 from 2 votes
French Onion Soup Casserole
Prep Time
10 mins
Cook Time
1 hr 30 mins
Total Time
1 hr 40 mins

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!

Course: Main Course
Cuisine: American
Keyword: French Onion Soup, French Onion Soup Casserole, Onion Casserole
Servings: 6 servings
Calories: 201.2 kcal
Author: Blair
  • 3 medium sweet onions, sliced
  • 3 tablespoons butter
  • 4 cups beef broth
  • 1 teaspoon Worcestershire sauce
  • 4 oz 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
  1. Melt butter in a large saucepan over low heat.
  2. Add onions and cover. Cook for about 30 minutes, stirring occasionally.
  3. Add the beef broth and the Worcestershire sauce. Heat the broth mixture until it boils.
  4. Reduce heat to low. Allow to simmer, uncovered, for about 30 minutes. The broth will reduce.
  5. 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).
  6. Lightly toast the slices of bread.
  7. Place toasted bread in a single layer on top of onion/broth mixture.
  8. Cover bread with a thick layer of the shredded mozzarella and top with grated Parmesan.
  9. Bake, uncovered, in a 350 degree oven for 20-30 minutes, or until cheese is melted and brown on top.
Recipe Notes

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!

Nutrition Facts
French Onion Soup Casserole
Amount Per Serving (1 /6 of the recipe)
Calories 201.2 Calories from Fat 86
% Daily Value*
Fat 9.5g15%
Saturated Fat 4.2g26%
Polyunsaturated Fat 0.3g
Monounsaturated Fat 3g
Cholesterol 31.5mg11%
Sodium 624.8mg27%
Potassium 108.4mg3%
Carbohydrates 16.1g5%
Protein 10.4g21%
* Percent Daily Values are based on a 2000 calorie diet.