Croque Monsieur Casserole

My neighbor knocked on my door one Sunday morning with leftover ham from her holiday dinner and a loaf of good white bread. She mentioned croque monsieur, and I thought of the sandwich, but she shook her head and described her grandmother's casserole version. An hour later, my kitchen smelled like a Parisian cafe, and I understood why she'd been so insistent. The creamy béchamel pooling into buttery bread, the sharp bite of Gruyère browning at the edges—it was comfort in a baking dish, no flipping required.

The first time I served this to friends, I worried it might be too rich for a casual Saturday lunch. But as we sat around the table with a simple green salad and cold white wine, scraping our plates clean, someone said it tasted like vacation. That stuck with me. It's the kind of dish that makes an ordinary morning feel a little more intentional, a little more indulgent.

Ingredients

• White sandwich bread: Removing the crusts isn't fussy, it's practical—they soak up the custard more evenly and bake into soft, golden layers instead of tough edges.
• Unsalted butter: You'll use it twice, once to grease the dish and again to brush the bread, creating those crispy, buttery pockets that make this casserole irresistible.
• Gruyère cheese: Its nutty, slightly sweet flavor is traditional, but Swiss works beautifully if that's what you have—just grate it fresh for the best melt.
• Whole milk and heavy cream: Together they create a custard that's rich without being heavy, binding everything into creamy, savory comfort.
• Large eggs: They give structure to the custard and help the casserole puff up beautifully in the oven.
• Cooked ham: Use deli ham or leftover holiday ham—it adds salty, savory depth that balances the creamy béchamel.
• All-purpose flour: The base of your béchamel, it thickens the sauce into a velvety blanket that coats every layer.
• Ground nutmeg: Just a whisper of it in the béchamel adds warmth and a subtle complexity that feels very French.
• Salt and black pepper: Season the béchamel generously, it's the flavor backbone of the entire dish.

Instructions

Prep the dish and oven:

Preheat your oven to 375°F and butter your baking dish generously. A well-greased dish prevents sticking and adds an extra layer of richness to the edges.

Make the béchamel:

Melt butter in a saucepan, whisk in flour until it smells toasty, then slowly add milk while whisking constantly to avoid lumps. Season with nutmeg, salt, and pepper, then set it aside to cool slightly.

Butter and layer the bread:

Butter one side of each slice, then arrange half the slices buttered side down in the dish. This creates a crispy bottom layer that holds up under all that creamy custard.

Build the layers:

Add half the ham and half the cheese, then repeat with remaining bread, ham, and cheese. Press gently as you go so everything nestles together.

Pour the custard:

Whisk together eggs, milk, cream, and a pinch of salt, then pour it evenly over the casserole, pressing down gently so the bread absorbs it. Let it sit for a minute or two if you have time.

Top with béchamel:

Pour the béchamel over everything and spread it gently with a spatula. It will settle into the layers and create a golden, bubbling top.

Bake and rest:

Bake uncovered for 35 to 40 minutes until puffed, golden, and bubbling at the edges. Let it rest for 10 minutes before serving so the custard sets and slicing is easier.

Save Pin

One morning I made this for my parents, and my dad, who never comments on food, paused mid-bite and said it reminded him of a cafe in Lyon where he ate lunch decades ago. I hadn't been aiming for nostalgia, but somehow this casserole unlocked it. That's the thing about simple, honest food—it travels through time without trying.

Making It Ahead

You can assemble the entire casserole the night before, cover it tightly with plastic wrap, and refrigerate it. In the morning, let it sit at room temperature for 20 minutes while the oven preheats, then bake as directed. The flavors meld overnight, and the bread soaks up even more custard, making it extra luscious.

Vegetarian and Flavor Swaps

Leave out the ham and add sautéed mushrooms or wilted spinach between the layers for a vegetarian version that's just as satisfying. A thin layer of Dijon mustard spread on the bread before layering adds a sharp, tangy kick that cuts through the richness beautifully. I've also used turkey, roasted chicken, and even leftover pork tenderloin with great results.

Serving and Pairing

This casserole is rich, so I always serve it with something bright and acidic to balance it out. A simple arugula salad with lemon vinaigrette, roasted asparagus, or even pickled vegetables on the side makes the meal feel complete. A crisp white wine like Chardonnay or a dry rosé is perfect, though I've enjoyed it just as much with strong coffee on a lazy Sunday.

• Pair with a green salad dressed in mustard vinaigrette for contrast.
• Serve alongside roasted tomatoes or sautéed greens for color and freshness.
• Leftovers reheat well in a 350°F oven, covered with foil, for about 15 minutes.

Save Pin

This casserole has become my answer to special mornings when I want something impressive but not stressful. It's forgiving, adaptable, and always makes people feel cared for.

Recipe Help & FAQs

→ Can I make this casserole ahead of time?

Yes, you can assemble the casserole up to 24 hours in advance. Cover tightly with plastic wrap and refrigerate. Add the béchamel sauce just before baking and extend the cooking time by 5-10 minutes if baking from cold.

→ What cheese works best as a substitute for Gruyère?

Swiss cheese is the closest substitute, offering a similar nutty, mild flavor. Emmental or Comté also work beautifully. For a sharper taste, try aged cheddar, though it will change the traditional French flavor profile.

→ How do I prevent the casserole from becoming soggy?

Remove the bread crusts and ensure each slice is buttered on one side to create a barrier. Don't oversoak the bread—pour the egg mixture evenly and press gently. Let the casserole rest 10 minutes after baking to set properly.

→ Can I freeze leftovers?

Yes, this casserole freezes well for up to 2 months. Cool completely, then wrap tightly in aluminum foil and plastic wrap. Thaw overnight in the refrigerator and reheat covered at 350°F until warmed through, about 20-25 minutes.

→ What can I serve alongside this casserole?

A crisp green salad with Dijon vinaigrette balances the richness perfectly. Fresh fruit, roasted asparagus, or a simple arugula salad also complement the dish beautifully. Pair with white wine like Chardonnay or a light Pinot Noir.

→ How do I make a vegetarian version?

Omit the ham and add sautéed mushrooms, caramelized onions, or wilted spinach between the bread layers. You can also use vegetarian ham alternatives available at most grocery stores for a similar texture and protein content.