Croque Monsieur Casserole

My brother-in-law showed up one Sunday with a bag of day-old bread and announced he was making breakfast. What emerged from the oven was this glorious, golden casserole that tasted like the best grilled cheese you ever had, but softer, richer, and somehow fancier. He called it his lazy Croque Monsieur, and I've been making it ever since. It's the kind of dish that makes people lean back in their chairs and ask for the recipe before they've even finished their first serving.

I made this for a friend's baby shower brunch, and it sat in the oven filling the house with the smell of butter and melted cheese while we opened gifts. By the time we cut into it, everyone was hovering around the table. One guest scraped the dish clean with a spatula and said it was better than anything she'd had in Paris, which I'm sure was an exaggeration, but I didn't argue.

Ingredients

• White sandwich bread: Day-old bread works best because it soaks up the custard without falling apart, and removing the crusts gives you those tender, custardy edges.
• Unsalted butter: You'll use it to grease the dish and butter each slice, which creates little pockets of richness throughout the casserole.
• Gruyere cheese: This is the cheese that makes a Croque Monsieur taste like itself, nutty and melty, though Swiss works in a pinch.
• Whole milk and heavy cream: The custard base that turns this into something between French toast and a savory bread pudding.
• Large eggs: They bind everything together and give the casserole structure as it bakes.
• Cooked ham: Use good deli ham or leftover holiday ham, anything with a bit of flavor and not too much water.
• All-purpose flour: The thickener for your bechamel, which adds that classic French creaminess on top.
• Ground nutmeg: Just a whisper of it in the bechamel makes everything taste more sophisticated.
• Salt and black pepper: Season every layer so the flavor builds as you go.

Instructions

Preheat and Prep Your Dish:

Set your oven to 375°F and butter a 9x13-inch baking dish generously, getting into the corners. This prevents sticking and adds another layer of buttery flavor to the edges.

Make the Bechamel:

Melt 2 tablespoons of butter in a saucepan over medium heat, whisk in the flour, and let it cook for a minute until it smells toasty. Slowly pour in the milk, whisking constantly, until the sauce thickens enough to coat the back of a spoon, then season it with nutmeg, salt, and pepper.

Butter the Bread:

Spread softened butter on one side of each slice of bread. This step feels a little fussy, but it's what makes the top golden and the inside impossibly rich.

Layer the Casserole:

Arrange half the bread slices buttered-side down in the dish, then layer on half the ham and half the cheese. Repeat with the remaining bread, ham, and cheese, pressing down gently so everything nestles together.

Pour the Custard:

Whisk together the eggs, milk, cream, and a pinch of salt, then pour it evenly over the casserole. Press down gently on the bread so it soaks up the liquid.

Add the Bechamel:

Pour the bechamel sauce over the top and spread it with a spatula to cover everything. It might seem like a lot, but it creates that creamy, golden top layer.

Bake Until Golden:

Slide the dish into the oven and bake for 35 to 40 minutes, until the top is puffed and bubbling and the edges are crispy. Let it rest for 10 minutes before cutting in, or you'll have a molten cheese disaster on your hands.

Save

The first time I served this, my cousin asked if I'd gone to culinary school. I laughed and told her it was just bread, cheese, and ham dressed up with a little butter and patience. She took another slice anyway.

Making It Ahead

You can assemble the entire casserole the night before, cover it tightly, and refrigerate it. In the morning, let it sit on the counter while the oven preheats, then bake as directed. The bread soaks up even more custard overnight, which makes it extra custardy and almost impossible to mess up.

Customizing the Filling

I've made this with sautéed mushrooms and spinach for a vegetarian version, and it was just as satisfying. You can also spread a thin layer of Dijon mustard on the bread before layering, or tuck in some caramelized onions if you want a little sweetness. Just don't overload it, or the custard won't set properly.

Serving Suggestions

This casserole is rich, so I like to serve it with a simple arugula salad dressed in lemon and olive oil to cut through the creaminess. A glass of crisp Chardonnay doesn't hurt either, though coffee works just as well if it's breakfast.

• Pair it with fresh fruit for a lighter brunch spread.
• Serve it with roasted asparagus or green beans for dinner.
• Leftovers reheat beautifully in the oven, covered with foil.

Save

This casserole has become my go-to whenever I need to feed people something comforting without spending the whole morning in the kitchen. It's fancy enough to impress, but forgiving enough that you can make it in your pajamas.

Recipe Questions & Answers

→ 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. Allow it to sit at room temperature for 30 minutes before baking, and add 5-10 minutes to the baking time if needed.

→ What type of bread works best for this dish?

White sandwich bread or pain de mie are ideal because they absorb the custard beautifully without becoming too dense. Brioche adds extra richness, while sourdough offers a tangy contrast.

→ Can I substitute the Gruyère cheese?

Swiss cheese is the closest substitute with a similar nutty flavor. Emmental, Comté, or a sharp white cheddar also work well, though they will slightly alter the traditional French character.

→ How do I make this vegetarian?

Omit the ham and add sautéed mushrooms, caramelized onions, or fresh spinach between the bread layers. A touch of Dijon mustard enhances the savory depth without meat.

→ Why is my casserole soggy instead of crispy?

Ensure the bread is buttered on one side and pressed gently into the custard without oversaturating. Baking uncovered at the correct temperature allows the top to crisp and brown properly.

→ What should I serve with this casserole?

A crisp green salad with Dijon vinaigrette balances the richness perfectly. Roasted asparagus, sautéed green beans, or a light arugula salad also complement the creamy, cheesy flavors beautifully.