TL;DR (Quick-Answer Box)
- What it is: A rich make-ahead breakfast bake featuring buttery croissants filled with Dijon mustard, deli ham, and Gruyère, soaked in a savory egg custard.
- Why you’ll love it: It transforms the classic French sandwich into an easy overnight casserole. It’s decadently creamy, cheesy, and perfect for feeding a hungry crowd.
- How to make it: Fill croissants with ham and cheese, cut into pieces, and soak in custard overnight. Top with homemade béchamel and bake until puffed.
Jump To
- TL;DR (Quick-Answer Box)
- Why this croque monsieur casserole recipe works
- Your croque monsieur casserole questions, answered
- Croque monsieur casserole pro tips & troubleshooting
- What to serve with croque monsieur
- Storage & reheating
- More sassy French bistro recipes
- Write a review
- Croque Monsieur Casserole Recipe
- Recipe Testers’ Reviews
The croque monsieur—that perennial French classic—is the little black dress of the bistro set. My first genuine one was at a little wedge of a bistro in Paris about 30 years ago. It was the perfect example of a bistro bite. But memories can fade, and frankly, I’ve never attempted the sandwich at home because I didn’t want to ruin the nostalgia.
Then came Costco.
If you know The One, you know he’s mad about buying in bulk. Our basement looks like we’re prepping for Armageddon. So when I found myself staring down a bag of croissants the size of a Fiat and a hunk of cheese the size of a hassock, I knew making individual sandwiches wouldn’t cut it. I decided to go all Betty Crocker on their asses.
If the croque monsieur is the little black dress, then using buttery croissants instead of white bread is the string of pearls it’s been missing. This casserole is insanely rich, decadently custardy, and features a homemade béchamel that I can still whip up in my sleep thanks to my time at the French Culinary Institute. (Take that, M. Sailhac!) This is THE brunch dish for when you want to look like a culinary badass but haven’t pounded back your three French presses yet.
Chow,
Featured Review
Indulgent! I was eating a croque madame at a cafe in Paris in 1974 when a student demonstration shut down all the adjacent streets for 3 hours (we were the only people in the cafe, and as I recall a lot of Carlsbergs were drunk while we waited for the barricades to be moved). Looking forward to wowing some brunch guests with this dish, a great excuse to tell my 50-year-old story again…
Holly Hughes
Why this croque monsieur casserole recipe works
The croissant upgrade is a game-changer. While traditional croque monsieurs rely on pain de mie or brioche, swapping in croissants adds layers of buttery, flaky texture that soak up the custard beautifully without falling apart. It turns a sandwich into a soufflé. Kinda.
It’s the ultimate make-ahead secret. I’m lazy. I designed this specifically as an overnight bake so I don’t have to think in the morning. The overnight chill allows the egg mixture to soak the croissants. That means you get soft, custardy insides while the edges bake up wildly crispy.
The classic Béchamel finish creates a bistro-quality crust. A silky, homemade Béchamel sauce is slathered on top before the final sprinkle of cheese. This creates a bubbling, golden, creamy topping that prevents the casserole from drying out and gives it that authentic French richness.
Your croque monsieur casserole questions, answered
A croque monsieur served with a poached or lightly fried egg on top is known as a croque madame (or, in parts of Normandy, as a croque à cheval). The name croque mademoiselle is associated with a lighter, vegetarian version that’s made of the same bread, but with ordinary melting cheese, accompanied with chives, cucumber, and green salad.
A monte cristo is another type of French sandwich, also made with ham and Gruyère. It is dipped in egg custard and pan fried. It is served with jam or syrup.
Indeedy you can. Bake the casserole and allow it to cool completely, wrap it in plastic, and then wrap it tightly with foil. The night before you plan on reheating the casserole, place it in the refrigerator to defrost overnight. Reheat the dish in a 325°F to 350°F (163°C to 175°C) oven until the temperature in the center is 165°F (74°C).
Now, I’ve gotten questions from some folks about whether you can use something other than croissants. My question always is, “Why?!” The answer is, yes, of course. But I’d suggest enriched bread, such as brioche or challah. You want that little bit of extra richness for this marvelous dish.
Croque monsieur casserole pro tips & troubleshooting
☞ Stale is the new fresh
Day-old croissants act like a sponge, soaking up the custard without turning to mush. If yours are fresh, let them dry out on the counter for a few hours.
☞ Don’t skip the press
Don’t just dump the eggs and run. Gently press the croissants down to force that liquid into every nook and cranny. No dry pockets allowed.
☞ Whisk that sauce
Add the milk to the roux slowly while whisking constantly to avoid lumps. If you do get lumps, just blitz it with an immersion blender. Your secret’s safe with me.
☞ The mustard matters
It provides the necessary acidity to cut through the insane richness of the ham and cheese. Don’t skip it, or the dish will feel too heavy.
What to serve with croque monsieur
If you’re going for a brunch vibe, whip up a sharply dressed green salad. A lemon vinaigrette is a must. A bowl of macerated berries (think strawberries, blackberries, blueberries) or an orange, apple and fennel salad is lovely.
If dinner’s more your style, char some cherry tomatoes on the vine in the oven until blistered. And I’d never say no to a platter of roasted root veggies.
Storage & reheating
Fridge: Leftovers will keep happily in the refrigerator for 3 to 4 days. Let the casserole cool completely before tightly covering with plastic or transferring it to an airtight container.
Freezer: The baked casserole will last for up to 2 months. Wrap individual slices (or the whole dish) in a layer of plastic wrap followed by a layer of foil to prevent freezer burn. Thaw it overnight in the fridge before reheating.
Reheating: For the best texture, pass on the microwave—it turns the croissants rubbery. Instead, place the casserole (or slices) in a 350°F (175°C) oven, covered with foil, for about 15 to 20 minutes. Remove the foil for the last 5 minutes to crisp up that cheesy top.
More sassy French bistro recipes
Write a review
If you make this recipe, or any dish on LC, consider leaving a review, a star rating, and your best photo in the comments below. I love hearing from you.–David
Featured Review
This caught my eye and stuck with me immediately when it was posted after Easter. I assembled it some time ago and I finally got around to baking it this morning. It was terrific! A great choice for a brunch menu. The only last minute part was making a fresh béchamel. I layered very thinly sliced shallot and snipped chives under the béchamel because, why not? For the meat and cheese I used rolled prosciutto and provolone appies also left over from Easter. Just placed them in the “sandwiches” as they were. All my leftovers simply and deliciously combined into brunch! I turned the broiler element on for the last several minutes. We had the casserole with slices of those long mini San Marazano cherry tomatoes from Trader Joe’s which I tossed with chives and lightly smoked salt. It all combined to an easy, delicious, memorable brunch.
Rainey
Croque Monsieur Casserole
Equipment
- 9-by-13-inch (23-by-33-cm) casserole dish
Ingredients
For the croque monsieur casserole
- Butter, for the dish
- 7 large croissants, (about 1 pound | 500 g)
- Your favorite Dijon mustard
- 14 slices deli ham, (about 8 ounces | 230 g)
- 8 ounces Gruyère, Emmenthaler, Jarlsberg, or Swiss cheese, grated (about 2 cups)
- 8 large eggs
- 2 cups whole milk
- Salt and freshly ground white pepper
For the béchamel sauce
- 3 1/4 cups whole milk
- 5 tablespoons (2 1/2 oz) unsalted butter
- 5 tablespoons all-purpose flour
- Pinch ground nutmeg
- Salt and freshly ground black pepper
Instructions
Make the croque monsieur casserole
- Butter a 9-by-13-inch (23-by-33-cm) casserole dish.
- Slice the croissants lengthwise and spread with a bit of mustard.
- Tuck 2 slices of ham and about 1/4 cup cheese inside each croissant.
- Cut each croissant into quarters, and fit the pieces in the dish. Turn them different ways, so some have frilly slices of ham showing.
- In a large bowl, whisk the eggs, then pour in the milk and whisk to combine. Season lightly with salt and pepper.
- Evenly pour the egg mixture over the croissant pieces. Press down with your hands to make sure all the liquid is absorbed. Cover with plastic wrap and refrigerate overnight.
Make the béchamel sauce
- In a medium saucepan over medium heat, warm the milk just until a skin begins to form on top, but the milk isn't boiling.
- Meanwhile, in another medium saucepan over medium heat, melt the butter. Add the flour and stir constantly until the mixture bubbles, about 2 minutes.
- Slowly pour the hot milk into the pan with the flour-butter mixture, whisking the whole time. Bring the mixture to a boil, then reduce to low and simmer until the béchamel thickens, 2 to 3 minutes more. Season with nutmeg, salt, and pepper.
- Pour the sauce into a container, press plastic wrap against the surface to prevent a skin from forming, and let cool to room temperature. Refrigerate overnight.
Assemble the casserole
- The next morning, remove the casserole and béchamel sauce from the refrigerator 30 minutes before baking. Crank the oven to 350°F (175°C).
- Uncover the casserole and place it on a foil-lined rimmed baking sheet. Using a whisk, stir the béchamel to loosen it. Spread the sauce over the top, and sprinkle with the remaining cheese.
- Bake the casserole until puffed and golden brown, 50 to 55 minutes.
- Serve immediately.
Notes
An LC Original
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Nutrition
Nutrition information is automatically calculated, so should only be used as an approximation.
Recipe Testers’ Reviews
Did you know only 68% of the recipes we test make it onto the site? This recipe survived our rigorous blind testing process by multiple home cooks. It earned the Leite’s Culinaria stamp of approval—and the testers’ reviews below prove it.
This croque monsieur casserole packs a wallop of cozy. So rich and creamy, it epitomizes “comfort food.” With ingredients like croissants, Gruyère, eggs, and ham—it’s a dreamy strata that is high on the rich and velvety quotient. So much so, that it’s a dish that’s perfect for entertaining and/or a special occasion, especially since you can prepare all the components ahead of time. I’d never eaten or prepared the classic croque monsieur dish but I had served a mushroom tartine version that had similar components and preparation. At the time, I suggested to my family that they should envision ham and cheese prepared the same way and they all swooned.
I could envision this dish being served for brunch, dinner, or part of a buffet. It’s also an ideal dish to share with neighbors and friends who recently had a baby or are going through a difficult time. What a gift of love this would be!
With over twenty-plus years with my husband, I know when he likes something I’ve cooked for him, when he’s not too thrilled with it, and when he REALLY loves it. This croque monsieur casserole would merit the REALLY-REALLY-loves-it category. How did I know? I never had to ask him what he thought of the dish. His Pavlovian response was “Mmmm, this is good,” as soon as the warm gooey mass hit his mouth. And the “Oh boy, I love this!” comment muttered under his breath a few times throughout the meal—as if I weren’t in the room with him—definitely gave it away.
I decided to make one change—I ended up turning this luscious dish into a croque madame, adding a creamy, dreamy over-easy egg (cooked in butter) on top of the wedge of deliciousness. Maybe that’s why hubby’s eyes rolled back in his head? Who knows? I do know I’ll be serving it again this week, sharing it with our neighbor, and making it again in the future—for brunch, lunch, and/or dinner. It would be a great potluck dish too!
I served it with a salad of butter lettuce, avocado, pistachios, orange segments, fresh dill and parsley, olive oil, red wine vinegar, salt, pepper, and the juice of the orange.
This croque monsieur casserole is a wonderful upgrade to more traditional egg/bread casseroles. The croissants give it a wonderful fluffy quality and the bechamel sauce adds a delicious richness.
It’s important to use good-quality ham so the flavor really comes through. It’s easily put together, and, because it’s refrigerated overnight, it makes for a stress-free morning. I made this for Sunday brunch and it was perfect with some fresh fruit and good coffee. I definitely recommend making this for guests.
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Ohmygosh, you were right, David! My fridge was too cold and the big dish must have been a heat sink. I made it again with stale cut-up croissants, divided into two 8-inch dishes, and it’s absolutely delicious. I’m taking the second dish to a sister who loves croque monsieur. Thank you so much for a wonderful brunch dish!
Phew, Ems! I was banging my head against the wall trying to figure out what could’ve gone wrong! I’m so delighted you made it again, and you have one lucky sister there!
We like it and will make again, maybe tonight. I refrigerated it overnight in a glass pan and then set it on the counter for 30 minutes before baking. It was still soupy and only 120 degrees when checked so baked it much longer to get to safe temp. Puzzled if glass slowed the cooking so much. (Yes, my oven temp is correct.)
Ems, first off, you were incredibly smart to use a thermometer—that was a genius move that saved breakfast. Good on you for trusting your instincts.
I have to be honest: I’m completely flummoxed by this. For something to be in the oven for almost an hour and only reach 120°F is utterly baffling. It sounds like the center was frozen or near frozen when it went in.
I’m just spitballing here, looking for any variable that could’ve caused this, because I’ve made this dish many times and never ran into this. Aside from the oven recovery (the oven registering the correct temperature before the food goes in but not getting back up to the temperature when it cycles), here are a few other culprits:
If the croissants were particularly large or dense (bakery vs. supermarket), or if they were packed in very tightly, the heat just wouldn’t penetrate to the center fast enough. Also, if the eggs were larger than standard “large” eggs, that adds more liquid volume to heat up.
Another thought: I know during the holidays I crank my refrigerator temperature down because I have so much food packed in there. If your fridge was extra cold, that heavy ceramic or glass dish would act like a massive heat sink, keeping the center raw while the oven tried to catch up.
I believe you that your oven is calibrated (and I know how frustrating it is when websites automatically blame the oven—it’s such an easy cop-out), but I suspect it just couldn’t recover the heat fast enough against that cold, dense mass. I’m sorry it gave you trouble, but I’m so glad you stuck with it and got it to the table safely!
Please let me know if you do make it again today how it turns out.