Overnight Croque Monsieur Casserole Recipe

Introduction

This Overnight Croque Monsieur Casserole transforms the classic French sandwich into a rich, savory breakfast bake. With layers of bread, Canadian bacon, Gruyere cheese, and a flavorful egg custard, it’s perfect for a make-ahead brunch that delights a crowd.

Ingredients

• 1 tablespoon unsalted butter, plus more to coat pan
• 1 yellow onion, roughly chopped (about 1 1/2 cups)
• 4 cloves garlic, thinly sliced
• Salt and pepper, to taste
• 1 tablespoon fresh thyme, roughly chopped, plus 1 teaspoon for garnish
• 8 large eggs
• 1 1/2 cups half-and-half
• 2 tablespoons Dijon mustard
• 1/2 teaspoon hot sauce, plus more for garnish
• 1 1/2 teaspoons kosher salt
• 1 loaf Martin’s Old-Fashioned Real Butter Bread, stale or toasted, cut into thick cubes
• 2 cups Gruyere cheese, shredded (about 4.5 ounces)
• 1/2 pound Canadian bacon, cut into 1/2-inch dice
• 1/4 cup Parmesan cheese, finely grated (about 1 ounce)

Instructions

1. Step 1: Butter a 3-quart (13×9-inch) baking dish and set aside.
2. Step 2: Heat a large frying pan over medium heat and add 1 tablespoon butter. When butter is frothy, add the chopped onion, season with salt, and cook until softened, about 3 to 4 minutes. Add garlic, season with salt and pepper, and cook until fragrant, about 1 minute. Remove from heat and stir in chopped thyme.
3. Step 3: In a large bowl, whisk together eggs, half-and-half, Dijon mustard, hot sauce, and kosher salt until evenly combined. Arrange half of the bread cubes in the bottom of the prepared baking dish. Sprinkle with 1 cup shredded Gruyere, half of the onion-garlic mixture, and half of the Canadian bacon. Repeat the layers with the remaining bread, onion mixture, ham, and Gruyere. Pour the egg mixture evenly over the layers.
4. Step 4: Press down on the bread to fully submerge it in the egg custard. Cover the dish with plastic wrap and weigh down with a heavy plate. Refrigerate for 3 to 12 hours.
5. Step 5: When ready to bake, remove the weight and plastic wrap. Cover casserole with foil and place on the middle rack of the oven. Set oven to 325°F (no preheating needed) and bake for 35 minutes. Remove foil, sprinkle Parmesan cheese over the top, increase temperature to 375°F, and bake for an additional 10 to 15 minutes until golden brown.
6. Step 6: Remove from oven and sprinkle with the remaining thyme. Let cool for at least 5 minutes before serving. Serve with additional hot sauce on the side if desired.

Tips & Variations

• Use stale or lightly toasted bread to help absorb the custard without becoming too soggy.
• Substitute Canadian bacon with ham or cooked pancetta for a different flavor.
• For a vegetarian version, omit the bacon and add sautéed mushrooms or spinach instead.
• Make sure to press down the bread well when soaking overnight for even custard absorption.

Storage

Store any leftover casserole covered in the refrigerator for up to 3 days. Reheat individual portions gently in the microwave or warm in a 350°F oven until heated through. This dish freezes well — wrap tightly and freeze for up to 2 months. Thaw overnight before reheating.

How to Serve

Serve this delicious recipe with your favorite sides.

FAQs

Can I prepare this casserole in the morning instead of overnight?

Yes, you can let the casserole soak for at least 1 hour before baking, but the flavors and custard texture improve with a longer soak of up to 12 hours.

Can I use a different type of bread for this recipe?

Absolutely. While butter bread or brioche provides richness and absorbs the custard well, sturdy white bread or sourdough can also work nicely.

Overnight Croque Monsieur Casserole Recipe

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★★★★★

4.7 from 77 reviews

This Overnight Croque Monsieur Casserole elevates the classic French sandwich into a hearty, make-ahead breakfast or brunch dish. Featuring layers of buttery bread, caramelized onions, garlic, Canadian bacon, Gruyere, and a creamy mustard-egg custard, it bakes to a golden, cheesy perfection. With a simple overnight soak, it’s perfect for busy mornings or entertaining guests.

• Author: Ria
• Prep Time: 20 minutes
• Cook Time: 50 minutes
• Total Time: 3 hours 20 minutes to 12 hours 20 minutes (including overnight soak)
• Yield: 12 servings 1x
• Category: Breakfast Casserole
• Method: Baking
• Cuisine: French-American

Ingredients

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Bread and Butter

• 1 Loaf Martin’s Old-Fashioned Real Butter Bread, stale or toasted, cut into thick cubes
• Unsalted Butter, plus more to coat pan (about 1 tablespoon plus extra for greasing)

Vegetables and Herbs

• 1 Yellow Onion, roughly chopped (about 1 1/2 cups)
• 4 Cloves Garlic, thinly sliced
• 1 Tablespoon Fresh Thyme, roughly chopped, plus 1 teaspoon for garnish
• Salt and Pepper, to taste

Dairy and Eggs

• 8 Large Eggs
• 1 1/2 Cups Half-and-Half
• 2 Cups Gruyere Cheese, shredded (about 4.5 ounces)
• 1/4 Cup Parmesan Cheese, finely grated (about 1 ounce)

Meat

• 1/2 Pound Canadian Bacon, cut into 1/2-inch dice

Other

• 2 Tablespoons Dijon Mustard
• 1/2 Teaspoon Hot Sauce, plus more for garnish
• 1 1/2 Teaspoons Kosher Salt

Instructions

1. Prepare the Baking Dish: Coat a 3-quart (13×9-inch) baking dish generously with butter to prevent sticking and set it aside for later use.
2. Sauté Onions and Garlic: Heat a large frying pan over medium heat and add 1 tablespoon unsalted butter. When the butter is slightly frothy, add the roughly chopped onion and season with salt. Cook until the onions are just softened, about 3 to 4 minutes. Add the thinly sliced garlic, season with salt and pepper, and cook for another minute until fragrant. Remove from heat and stir in the fresh thyme.
3. Mix the Custard: In a large bowl, whisk together the eggs, half-and-half, Dijon mustard, hot sauce, and kosher salt until the mixture is smooth and uniform.
4. Layer the Casserole: Arrange half of the cubed butter bread evenly in the bottom of the prepared baking dish. Sprinkle with 1 cup of shredded Gruyere cheese and half of the sautéed onion-garlic mixture and diced Canadian bacon. Repeat the layers with the remaining bread, onion mixture, Canadian bacon, and Gruyere cheese. Pour the egg custard evenly over the top.
5. Soak Overnight: Press down on the bread gently to fully submerge it in the egg custard. Cover the dish tightly with plastic wrap and place a heavy plate on top to weigh it down. Refrigerate the casserole for 3 to 12 hours to allow the bread to absorb the custard.
6. Bake Covered: When ready to bake, remove the plastic wrap and weight. Cover the casserole with aluminum foil and place it on the middle rack of the oven. Set the oven temperature to 325°F (no need to preheat) and bake for 35 minutes.
7. Bake Uncovered and Finish: Remove the foil, sprinkle the finely grated Parmesan cheese over the casserole, then increase the oven temperature to 375°F. Bake for an additional 10 to 15 minutes until the top is golden brown and bubbly.
8. Garnish and Serve: Remove the casserole from the oven and sprinkle the remaining fresh thyme on top. Let it cool for at least 5 minutes before serving. Offer additional hot sauce on the side for those who enjoy a spicy kick.

Notes

• Use stale or toasted bread to ensure it soaks up the custard well without becoming too soggy.
• Letting the casserole soak overnight improves flavor and texture, but a minimum of 3 hours will work in a pinch.
• Gruyere cheese provides classic nutty flavor; substitutions like Emmental or Jarlsberg can be used if unavailable.
• Adjust hot sauce to your heat preference or omit for a milder dish.
• You can prepare the casserole entirely in advance and refrigerate before baking for convenience.

Keywords: Croque Monsieur, breakfast casserole, make-ahead brunch, French breakfast, egg custard bake, Gruyere cheese, Canadian bacon