Croque Monsieur Casserole

The smell of nutmeg and melted Gruyère is what stopped me in my tracks at a tiny café outside Lyon. I watched the cook pull a bubbling golden casserole from the oven, and I knew I had to recreate it at home. After a few trials and one slightly burned top, I figured out the trick: press the bread gently into the custard so every layer soaks up that creamy richness. Now it's my go-to when I want to impress without spending all morning in the kitchen. It tastes like a fancy French bistro, but it's honestly just assembly and patience.

I made this for my sister's birthday brunch last spring, and she still talks about it. She's not usually one for casseroles, but the golden crust and the way the custard held everything together won her over. We ate it straight from the dish with a simple arugula salad on the side, and the whole table went quiet for a few minutes. That's how I knew it was a keeper.

Ingredients

• White sandwich bread: The soft texture soaks up the custard perfectly, and removing the crusts gives it a more refined, melt-in-your-mouth feel.
• Unsalted butter: Brushing it on the bread adds richness and helps create those crispy golden edges that contrast with the creamy center.
• Gruyère cheese: This is the star, it melts beautifully and has a nutty, slightly sweet flavor that defines the dish.
• Whole milk and heavy cream: Together they make the custard silky and luxurious without being too heavy or too thin.
• Large eggs: They bind the custard and give the casserole structure so it holds its shape when you slice into it.
• Cooked ham: Use good quality deli ham or leftover holiday ham, the saltiness balances the creamy layers.
• All-purpose flour: It thickens the béchamel and keeps it smooth and velvety when you pour it over the top.
• Ground nutmeg: Just a pinch transforms the béchamel from plain white sauce into something warm and deeply French.
• Salt and black pepper: Season every layer lightly, it builds flavor without overwhelming the delicate cheese and custard.

Instructions

Preheat and Prep the Dish:

Set your oven to 375°F and butter your baking dish generously so nothing sticks. This step seems small, but it makes cleanup so much easier later.

Make the Béchamel:

Melt the butter, whisk in the flour, and let it bubble for a minute to cook out the raw taste, then slowly add the milk while whisking constantly until it thickens into a smooth, glossy sauce. Season it well with nutmeg, salt, and pepper, the nutmeg is essential.

Butter the Bread:

Spread softened butter on one side of each slice and arrange half of them buttered side down in the dish. The buttered side against the pan creates a crispy bottom layer.

Layer Ham and Cheese:

Place half the ham over the bread, then sprinkle half the Gruyère, repeat with the remaining bread, ham, and cheese. Press down gently as you go so the layers nestle together.

Pour the Custard:

Whisk the eggs, milk, cream, and a pinch of salt, then pour it evenly over the casserole and press the bread down so it soaks up the liquid. Let it sit for a few minutes if you have time.

Top with Béchamel:

Pour the warm béchamel over everything and spread it gently with a spoon. It will settle into the gaps and create a golden, bubbly top.

Bake Until Golden:

Bake uncovered for 35 to 40 minutes until the top is puffed and deeply golden. Let it rest for 10 minutes before serving so the layers set and you can slice it cleanly.

Save

One rainy Sunday, I made this casserole and we ate it in our pajamas with nothing but coffee and good conversation. It felt indulgent and cozy at the same time, like we'd stolen a moment from a French countryside inn. That's the magic of this dish, it turns an ordinary day into something worth remembering.

Make It Your Own

If you want to skip the ham, sauté some mushrooms with garlic and layer them in instead, or use fresh spinach for a lighter vegetarian version. I've also spread a thin layer of Dijon mustard on the bread before layering, and it adds a subtle sharpness that cuts through the richness. You can even swap the Gruyère for a good Swiss or white cheddar if that's what you have on hand.

Timing and Storage

This casserole is perfect for entertaining because you can assemble it the night before, cover it tightly, and refrigerate it until you're ready to bake. Just add an extra 5 to 10 minutes to the baking time if it goes in cold. Leftovers keep well in the fridge for up to three days, and they reheat beautifully in a low oven or even the microwave.

Serving Suggestions

I love serving this with a simple green salad dressed in lemon vinaigrette, the acidity balances the creamy richness. A glass of chilled Chardonnay or a light Pinot Noir pairs beautifully if you're feeling fancy. It's also wonderful with roasted asparagus or a handful of fresh herbs scattered on top right before serving.

• Serve it family style straight from the baking dish for a relaxed, communal feel.
• Cut it into squares and plate individually with a small salad on the side for a more elegant presentation.
• Pair it with crusty baguette and soft butter if you want to lean into the French bistro vibe.

Save

This casserole has become one of those recipes I turn to when I want comfort and celebration in equal measure. I hope it brings you as much warmth and joy as it's brought to my table.

Recipe FAQs

→ Can I prepare this casserole ahead of time?

Yes, assemble the casserole up to 24 hours in advance, cover tightly with plastic wrap, and refrigerate. Pour the béchamel sauce over just before baking and add 5-10 minutes to the cooking time if baking straight from the refrigerator.

→ What cheese can I use instead of Gruyère?

Swiss cheese is the closest substitute with a similar nutty, mild flavor. Emmental, Comté, or a combination of fontina and Parmesan also work beautifully in this casserole.

→ How do I know when the casserole is fully cooked?

The casserole is done when the top is golden brown and puffed, the edges are bubbling, and a knife inserted in the center comes out clean. The internal temperature should reach 160°F (71°C).

→ Can I make this vegetarian?

Absolutely. Omit the ham and add sautéed mushrooms, caramelized onions, or blanched spinach between the bread layers for a delicious meat-free version that maintains the rich, savory character.

→ What bread works best for this casserole?

Classic white sandwich bread is traditional, but brioche adds extra richness, while sourdough provides a pleasant tang. Choose a sturdy bread that will hold up to the custard without becoming too soggy.

→ How should I store and reheat leftovers?

Store covered in the refrigerator for up to 3 days. Reheat individual portions in the microwave for 1-2 minutes, or cover the entire dish with foil and warm in a 325°F oven for 15-20 minutes until heated through.