Can I add meat to this French onion soup casserole?

Absolutely. For a hearty twist, add shredded rotisserie chicken for a french onion soup chicken casserole variation, or use thin slices of leftover roast beef for a comforting beef french onion soup casserole . Just layer it in with the onions and bread.

Can I use a different type of onion?

Yes, though I prefer sweet Vidalia onions for their gentle flavor, you can use yellow onions or even a mix. The key is to caramelize them slowly to bring out their natural sweetness.

How do I store and reheat leftovers?

Store in an airtight container in the fridge for up to 3 days. Reheat in the oven at 350°F, covered with foil, for about 20 minutes. Remove the foil during the last few minutes for a crispy top.

Can I make this into a rice casserole with French onion soup?

Yes, you can. Cook 1 cup of rice separately and stir it into the onion mixture before layering. It makes a delicious rice casserole with French onion soup that’s a little heartier and stretches further for families.

French Onion Soup Casserole That Feels Like a Warm Hug

Ingredients

Scale

Onion Base

1/4 cup unsalted butter
5 medium Vidalia onions, thinly sliced (about 3 lb.)
2 tsp kosher salt
1/2 tsp black pepper
3 thyme sprigs
2 flat-leaf parsley sprigs
2 bay leaves

Bread & Thickener

1 (16-oz) baguette, thinly sliced
1/3 cup all-purpose flour

Liquids

3 cups reduced-sodium beef broth
1/2 cup sherry

Cheese & Garnish

8 oz Gruyère cheese, shredded (about 2 cups)
1 tsp fresh thyme leaves

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Instructions

Caramelize the Onions
Melt butter in a Dutch oven over medium-low heat. Add onions, salt, and pepper. Cook slowly, stirring often, for 45–55 minutes until deeply golden.
Infuse with Herbs
Tie thyme sprigs, parsley, and bay leaves into a bundle with kitchen twine. Add during the last 15 minutes of caramelizing, then discard.
Toast the Bread
Preheat oven to 375°F. Arrange baguette slices on a baking sheet and toast for 10 minutes, flipping halfway.
Create the Broth Base
Stir flour into onions and cook 2 minutes. Gradually whisk in beef broth and sherry. Simmer 5–7 minutes until slightly thickened.
Assemble the Casserole
In a 9×13″ dish, layer half the onion mixture, followed by half the baguette and cheese. Repeat with remaining layers.
Bake and Serve
Bake uncovered for 20–25 minutes until cheese is bubbly and golden. Sprinkle fresh thyme on top and serve warm.

Notes

Use day-old bread for better texture.
Gruyère can be swapped with Swiss cheese if needed.
Add cooked chicken or roast beef for a protein-packed variation.
Best served with a green salad or roasted vegetables.

Author: Chef Sofia
Prep Time: 20 minutes
Cook Time: 1 hour 10 minutes
Category: Main Course
Method: Baked
Cuisine: French-American
Diet: Vegetarian

Nutrition

Serving Size: 1/6 of dish
Calories: 420
Sugar: 5g
Sodium: 580mg
Fat: 21g
Saturated Fat: 12g
Unsaturated Fat: 8g
Trans Fat: 1g
Carbohydrates: 38g
Fiber: 3g
Protein: 18g
Cholesterol: 55mg