Croque Monsieur Casserole

My neighbor Sophie knocked on my door one Saturday morning holding a casserole dish still warm from her oven. She'd made too much, she said, and thought I might like to try her grandmother's trick for turning Croque Monsieur into something you could serve a whole table. One bite and I was standing in a Parisian café, except I was in my pajamas with coffee going cold. I asked for the recipe immediately, scribbled it on the back of an envelope, and have been making it ever since for anyone who needs convincing that brunch can be both effortless and impressive.

I made this for my book club once, and the conversation stopped entirely for the first ten minutes. We just ate in silence, scraping our plates, until someone finally said, "I thought we were supposed to discuss the novel." It became the official dish for our meetings after that. Now when I pull it out of the oven, I know I have about fifteen minutes before anyone will care about plot or character development.

Ingredients

• White sandwich bread: Removing the crusts makes the casserole tender and custardy instead of chewy, and it soaks up the egg mixture like a dream.
• Unsalted butter: You'll use it to grease the dish, butter the bread, and make the béchamel, so don't skimp or substitute with margarine.
• Gruyère cheese: This is the soul of the dish with its nutty, slightly sweet flavor that melts into silk. Swiss works in a pinch, but Gruyère is worth the splurge.
• Whole milk and heavy cream: The combination creates a custard that's rich but not heavy, binding everything together without turning it soggy.
• Large eggs: They transform the milk and cream into a savory custard that puffs up beautifully in the oven.
• Cooked ham: Use good deli ham or leftover holiday ham. Avoid honey-glazed versions unless you want a sweet surprise.
• All-purpose flour: This thickens the béchamel and gives it body so it doesn't just run off into the casserole.
• Ground nutmeg: A tiny amount adds warmth and a whisper of something you can't quite name but will miss if you leave it out.
• Salt and black pepper: Season every layer, the béchamel, the custard, even a pinch between the bread, or the whole thing will taste flat.

Instructions

Rinse produce, clean cookware, and fill pots smoothly with flexible spray options for everyday cooking.

Check price on Amazon

Prep your dish and oven:

Preheat your oven to 375°F and butter your baking dish generously so nothing sticks. This step matters more than you think.

Make the béchamel:

Melt the butter, whisk in the flour until it smells toasty, then slowly add the milk while whisking constantly to avoid lumps. It should coat the back of a spoon when it's ready, thick and glossy with that nutmeg warmth stirred in.

Butter and layer the bread:

Spread soft butter on one side of each slice, then lay half of them buttered side down in the dish. This creates little pockets of richness that crisp up at the edges.

Add ham and cheese:

Lay half the ham over the bread, then scatter half the grated Gruyère on top. Repeat with the remaining bread, ham, and cheese, building flavors in every bite.

Pour the custard:

Whisk together the eggs, milk, cream, and a pinch of salt, then pour it evenly over everything and press gently so the bread drinks it all in. Let it sit for a minute or two if you have time.

Top with béchamel and bake:

Spoon the béchamel over the top and spread it gently to cover. Bake uncovered until the top is puffed and golden, with bubbles breaking through the surface, about 35 to 40 minutes.

Rest before serving:

Let it sit for 10 minutes after baking so the layers settle and you don't burn your mouth. This also makes it easier to cut into neat squares.

Pin It

The first time I served this to my father-in-law, he asked if I'd trained in France. I laughed and told him I'd just followed Sophie's envelope instructions and trusted the butter. He had three servings and asked if I'd make it for his birthday. It's become our tradition now, and every year he pretends he's surprised when I carry it to the table.

Making It Ahead

Assemble the entire casserole the night before, cover it tightly with plastic wrap, and refrigerate. In the morning, let it sit on the counter while the oven preheats, then bake as directed. You might need an extra 5 minutes since it's starting cold. I do this almost every time now because mornings are chaotic enough without whisking béchamel before coffee.

Swaps and Variations

Leave out the ham and tuck in sautéed mushrooms, caramelized onions, or wilted spinach for a vegetarian version that's just as satisfying. A thin smear of Dijon mustard between the bread layers adds a sharp little kick that makes people ask what your secret is. I've also used challah or brioche when I had it on hand, and the sweetness played beautifully against the salty cheese.

Serving Suggestions

This casserole is rich, so balance it with something bright and crisp. I serve it with a simple green salad dressed in lemon vinaigrette, or roasted asparagus when it's in season. A chilled glass of Chardonnay or a light Pinot Gris makes it feel like a proper French meal, even if you're eating it in sweatpants.

• Pair with a bitter green salad tossed with Dijon vinaigrette to cut through the richness.
• Serve alongside fresh fruit like sliced pears or grapes for a touch of sweetness.
• Offer crusty baguette on the side for anyone who wants to mop up every last bit of béchamel.

Rinse produce, fill pots, and clean cookware easily with flexible spray options for everyday cooking tasks.

Check price on Amazon

Pin It

This casserole has become my answer to lazy Sundays, surprise guests, and mornings when I want something special without the fuss. I hope it finds a place at your table the way it has at mine.

Recipe FAQs

→ Can I prepare this casserole ahead of time?

Yes, you can assemble the entire casserole up to 24 hours in advance. Cover tightly with plastic wrap and refrigerate. When ready to bake, let it sit at room temperature for 20 minutes, then bake as directed, adding 5-10 extra minutes if needed.

→ What cheese can I substitute for Gruyère?

Swiss cheese is the closest substitute and works beautifully. Emmental, Comté, or even sharp white cheddar will also deliver excellent results, though the flavor profile will vary slightly from the traditional French preparation.

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

The casserole is done when it's puffed up, golden brown on top, and bubbling around the edges. A knife inserted in the center should come out mostly clean, and the internal temperature should reach 160°F (71°C).

→ Can I make this without ham for a vegetarian version?

Absolutely. Simply omit the ham and add sautéed mushrooms, wilted spinach, or roasted vegetables between the bread layers. You can also add a touch of Dijon mustard for extra depth of flavor.

→ What type of bread works best for this dish?

Classic white sandwich bread is traditional and soaks up the custard beautifully. Brioche adds extra richness, while sourdough provides a tangy contrast. Avoid bread that's too dense or crusty, as it won't absorb the liquid mixture properly.

→ 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 warm the entire dish covered with foil in a 325°F (165°C) oven for 15-20 minutes until heated through.