The Best Onion Soup Casserole Recipe for Cozy Family Dinners

Hearty onion soup casserole redefines a classic comfort dish into a delightful baked experience that warms both body and soul.

Rich, golden-brown caramelized onions mingle with robust seasonings, creating layers of intense flavor and depth.

Melted cheese blankets the surface, forming a crispy, golden crust that promises pure indulgence.

Each spoonful tells a story of slow-cooked goodness and culinary tradition.

The aroma alone will draw hungry diners to the kitchen, anticipating a meal that feels like a warm embrace.

Rustic and elegant, this casserole elevates a simple ingredient into something extraordinary.

Prepare to fall in love with comfort food that satisfies completely.

Onion Soup Casserole: A Savory Classic with a Twist

• Slow-Caramelize Onion Magic: Patiently cooking onions for an hour develops deep, rich flavors that transform this simple ingredient into a luxurious base, creating a taste sensation that elevates the entire dish.
• Comfort Food Meets Gourmet Technique: Layering toasted baguette with caramelized onions and melted cheese creates a sophisticated twist on classic French onion soup, delivering restaurant-quality comfort right in your home kitchen.
• Quick-Prep Weeknight Showstopper: Despite its impressive appearance, this casserole comes together easily with straightforward steps, making it perfect for busy home cooks who want a delicious meal without complicated techniques.
• Nutritional Powerhouse in Disguise: Packed with 18g of protein and balanced macronutrients, this dish offers a satisfying meal that feels indulgent while providing substantial nutritional value.

Essential Ingredients for Onion Soup Casserole

• Onions: Sweet and flavorful base for the soup casserole, caramelized to develop rich, deep flavor. Yellow or white onions work best for this recipe.
• Baguette: Crusty French bread that provides a delightful texture and soaks up the onion mixture beautifully. Day-old bread works perfectly for better absorption.

• Butter: Adds richness and helps caramelize onions with a golden, smooth texture. Unsalted butter gives better control of the dishs saltiness.
• Cheese: Melts into a golden, bubbly topping that adds creamy and savory notes. Gruyère or Swiss cheese recommended for authentic French-style flavor.

• Broth: Provides deep, savory liquid base that creates the soups rich consistency. Beef or chicken broth both work well.
• Sherry: Adds depth and complexity to the overall flavor profile. Dry sherry preferred for best taste.
• Salt and Pepper: Essential seasonings that enhance the natural flavors of the ingredients.
• Thyme and Parsley: Fresh herbs that contribute aromatic and earthy undertones to the dish.
• Bay Leaves: Adds subtle background flavor and complexity to the onion base.
• Flour: Helps thicken the soup mixture and create a creamy consistency.

How to Make a Perfect Onion Soup Casserole

Step 1: Caramelize Onions

• Onions
• Salt
• Pepper
• Thyme
• Parsley sprigs
• Bay leaves

Cook for 1 hour, stirring frequently until onions turn golden brown and develop a rich, sweet flavor.

Step 2: Prepare Baguette Slices

Preheat oven to 350°F. Arrange baguette slices on a baking sheet. Toast for 12 minutes until crisp and lightly golden.

Step 3: Create Soup Base

Remove thyme, parsley, and bay leaves from the caramelized onions. Sprinkle flour over onions and cook for 2 minutes, stirring constantly. Pour in broth and sherry, bringing the mixture to a boil. Simmer for 2-3 minutes until the sauce thickens and becomes smooth.

Step 4: Assemble Casserole

• Placing half of the toasted baguette slices at the bottom
• Spooning onion mixture over the bread
• Adding remaining baguette slices on top
• Sprinkling cheese generously across the surface

Cover the dish with aluminum foil.

Step 5: Bake and Finish

Bake the casserole for 30 minutes. Remove foil and broil for 3 minutes until cheese becomes bubbly and slightly golden. Garnish with fresh thyme leaves for a fragrant final touch.

Tips for Baking the Perfect Onion Soup Casserole

• Caramelize Onions Slowly: Take your time cooking onions on low heat to develop deep, rich flavor without burning them.
• Choose Quality Cheese: Select a flavorful Gruyère or Swiss cheese that melts beautifully and creates a golden, crispy top.
• Toast Bread Perfectly: Cut baguette slices evenly and toast until golden and crisp to prevent soggy layers in the casserole.
• Use Fresh Herbs: Opt for fresh thyme and parsley to enhance the soup's aromatic profile and add brightness to the dish.
• Control Liquid Consistency: Stir broth and sherry carefully while cooking to achieve the ideal thickness for a creamy, luxurious texture.

How to Store and Reheat Onion Soup Casserole

• Refrigerate: Store leftover casserole in an airtight container within 2 hours of cooking. Seal tightly and keep in the refrigerator for up to 3-4 days. Cover with plastic wrap or lid to prevent moisture loss and protect from absorbing other food odors.
• Freeze: Transfer cooled casserole to a freezer-safe container or heavy-duty freezer bag. Label with date and contents. Frozen casserole can last up to 2 months. Wrap carefully to prevent freezer burn and maintain quality.
• Reheat: Thaw overnight in the refrigerator before reheating. Warm in a 350°F oven covered with foil for 20-25 minutes. Check internal temperature reaches 165°F for food safety. For best texture, avoid microwaving which can make bread soggy and cheese rubbery.

Best Sides to Serve with Onion Soup Casserole

• Elevate Classic Wine Pairing: Choose a crisp French white like Chablis or a medium-bodied Chardonnay to complement the rich, caramelized onion flavors and cut through the creamy cheese.
• Craft Beer Companion: Select a Belgian-style amber ale or a malty Oktoberfest beer that matches the sweet onion undertones and provides a robust backdrop to the casserole's depth.
• Fresh Salad Balance: Prepare a light arugula salad with lemon vinaigrette to contrast the heavy, savory casserole and refresh the palate between bites, adding a zesty, green counterpoint.
• Herb-Infused Side Suggestion: Create a simple green herb salad with fresh parsley, chives, and tarragon to enhance the herbaceous notes already present in the dish and provide a clean, bright accompaniment.

Fun Variations on Onion Soup Casserole

• French Alpine Fusion: Replace baguette with rustic mountain bread, add Swiss gruyère cheese, and sprinkle crushed alpine herbs for a hearty alpine-inspired version.
• Smoky Caramelized Rendition: Incorporate caramelized bacon bits into onion mixture, use smoked gouda cheese, and add a touch of bourbon instead of sherry for deep, rich flavors.
• Vegetarian Mediterranean Spin: Substitute beef broth with vegetable broth, mix in roasted red peppers, crumble feta cheese on top, and garnish with fresh oregano leaves for a Mediterranean-inspired casserole.
• Spicy Southwestern Style: Add diced green chiles to onion mixture, use pepper jack cheese, replace sherry with tequila, and top with crispy tortilla strips for a zesty southwestern flair.

Onion Soup Casserole Recipe

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4.9 from 12 reviews

• Total Time: 2 hours 5 minutes
• Yield: 6 1x

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Description

Hearty French onion soup meets comforting casserole in this delightful culinary fusion. Layers of caramelized onions, rich broth, and melted cheese create a soul-warming dish you’ll savor down to the last delicious bite.

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Ingredients

Scale 1x2x3x

Main Ingredients:

• 5 medium Vidalia onions, thinly sliced (about 1.36 kilograms or 3 pounds)
• 1 (16 ounces or 454 grams) baguette, thinly sliced
• 8 ounces (226 grams) Gruyère cheese, shredded (about 2 cups)
• 3 cups reduced-sodium beef broth

Seasoning and Herbs:

• 2 teaspoons kosher salt
• ½ teaspoon black pepper
• 3 thyme sprigs
• 2 flat-leaf parsley sprigs
• 2 bay leaves
• 1 teaspoon fresh thyme leaves

Fats and Liquids:

• ¼ cup unsalted butter
• ⅓ cup all-purpose flour
• ½ cup sherry

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Instructions

1. Caramelize the onions by melting butter in a Dutch oven over medium-low heat (about 60°F to 75°F). Incorporate whole onions, kosher salt, fresh ground black pepper, dried thyme, parsley sprigs, and bay leaves into the melted butter.
2. Slowly cook the onion mixture for approximately 60 minutes, stirring every 10 minutes to ensure even browning and prevent burning. The onions should transform into a rich, golden-brown color with a deep, sweet flavor profile.
3. Preheat the oven to 350°F (177°C). Slice the baguette into thin, uniform pieces and arrange them on a clean baking sheet in a single layer.
4. Toast the baguette slices for 12 to 15 minutes until they become crisp and light golden, creating a crunchy base for the casserole.
5. Remove the herb sprigs and bay leaves from the caramelized onions. Sprinkle all-purpose flour over the onions and cook for 2 minutes, stirring continuously to create a smooth roux.
6. Gradually pour in beef broth and dry sherry, stirring constantly. Bring the mixture to a rolling boil and cook for 2 to 3 minutes until the sauce thickens and becomes glossy.
7. Select a 13 x 9-inch (33 x 23 centimeters) baking dish and create the first layer using half of the toasted baguette slices, arranging them to cover the bottom completely.
8. Carefully spoon the rich onion mixture over the first bread layer, ensuring even distribution. Top with the remaining baguette slices.
9. Generously sprinkle grated Gruyère or Swiss cheese over the top layer, covering the entire surface.
10. Cover the baking dish with aluminum foil and bake in the preheated oven for 25 to 30 minutes.
11. Remove the foil and switch the oven to broil. Broil for 2 to 3 minutes until the cheese becomes bubbly and develops a golden-brown crust.
12. Garnish with freshly chopped thyme leaves and serve immediately while hot and aromatic.

Notes

• Slow-caramelized onions transform this classic soup into a hearty, comforting casserole that captures deep, rich flavor profiles.
• Toasting baguette slices beforehand ensures a crispy texture that perfectly absorbs the luxurious onion broth.
• Layering bread and onion mixture creates delightful pockets of concentrated taste throughout the dish.
• Sherry adds unexpected depth and complexity, elevating the traditional onion soup experience.
• Broiling at the end helps develop a golden, crispy cheese crust that looks as amazing as it tastes.
• Fresh thyme leaves sprinkled on top provide a bright, herbal finish that cuts through the richness.

• Prep Time: 1 hour 20 minutes
• Cook Time: 45 minutes
• Category: Dinner, Appetizer
• Method: Baking
• Cuisine: French

Nutrition

• Serving Size: 6
• Calories: 550 kcal
• Sugar: 3g
• Sodium: 900mg
• Fat: 25g
• Saturated Fat: 15g
• Unsaturated Fat: 8g
• Trans Fat: 0g
• Carbohydrates: 65g
• Fiber: 4g
• Protein: 18g
• Cholesterol: 60mg