Croque Monsieur Casserole

My mother-in-law showed up unannounced one Sunday morning with a bakery bag full of day-old bread and a block of Gruyère she'd found on sale. She refused to leave until we'd assembled this casserole together, her hands moving quickly as she tucked ham between buttery slices and poured béchamel like it was second nature. The kitchen smelled like a Parisian café by the time it came out of the oven. I've been making it ever since, though I still can't fold the bread corners as neatly as she does.

I made this for a brunch potluck once and watched three people go back for thirds. One friend, who claimed she didn't like ham, scraped her plate clean and asked for the recipe before she even finished chewing. It's become my go-to when I need to feed a crowd without the stress of flipping individual sandwiches or timing everything perfectly.

Ingredients

• White sandwich bread: Day-old bread actually works better here because it soaks up the custard without turning to mush, and removing the crusts helps everything bake evenly.
• Unsalted butter: Softening it first makes spreading a breeze, and using unsalted lets you control the seasoning since the ham and cheese already bring plenty of salt.
• Gruyère cheese: This is where the nutty, slightly sweet flavor comes from, though Swiss works in a pinch if Gruyère feels too fancy or expensive.
• Whole milk and heavy cream: The combination creates a custard that's rich but not so heavy you feel weighed down after one serving.
• Large eggs: They bind everything together and give the casserole that soufflé-like puff when it bakes.
• Cooked ham: I usually grab deli ham and ask them to slice it a little thicker, which holds up better during baking.
• All-purpose flour: It thickens the béchamel just enough to coat the back of a spoon without feeling gloppy.
• Ground nutmeg: Just a whisper of it makes the whole dish taste more complex without anyone being able to pinpoint why.
• Salt and black pepper: Taste as you go, especially with the béchamel, because underseasoned sauce makes the whole casserole taste flat.

Instructions

Get the oven ready:

Preheat to 375°F and butter your baking dish generously so nothing sticks to the edges when you serve it. I learned this the hard way after scraping half the cheese off the sides of an ungreased dish.

Make the béchamel:

Melt butter in a saucepan, whisk in flour, and let it bubble for a minute until it smells toasty. Pour in the milk slowly while whisking constantly so no lumps form, then cook until it coats the back of your spoon and season with nutmeg, salt, and pepper.

Butter and layer the bread:

Spread softened butter on one side of each slice, then lay half of them buttered side down in the dish. They should fit snugly but don't need to be perfect.

Add the fillings:

Layer half the ham and half the cheese over the bread, then repeat with the remaining bread, ham, and cheese. Press down gently so everything nestles together.

Pour the custard:

Whisk eggs, milk, cream, and a pinch of salt in a bowl, then pour it evenly over the casserole. Use your fingers to press the bread down so it soaks up the liquid.

Top with béchamel:

Pour the sauce over everything and spread it with a spoon or offset spatula. It will look like too much, but it bakes down into a golden, bubbling top layer.

Bake until golden:

Slide it into the oven uncovered and bake for 35 to 40 minutes, until the top is puffed and deeply golden. Let it rest for 10 minutes before cutting so the custard sets and you get clean slices instead of a soupy mess.

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The first time I served this to my book club, we completely forgot to discuss the book. Everyone was too busy scraping their forks across their plates and debating whether the nutmeg was the secret or if it was just the sheer amount of cheese. That's when I realized some recipes are worth more than the sum of their ingredients.

Making It Ahead

You can assemble the entire casserole the night before, cover it tightly with plastic wrap, and refrigerate it until you're ready to bake. Just add an extra 5 to 10 minutes to the baking time since it's going into the oven cold. I do this almost every time I make it for brunch because it means I can actually sit with my coffee instead of hovering over the stove.

Swaps and Variations

If you want to skip the ham, sautéed mushrooms or wilted spinach work beautifully and add a bit of earthiness. A thin layer of Dijon mustard spread on the bread before you add the ham gives it that classic croque monsieur tang. Some people like to add a handful of fresh thyme to the béchamel, which I've tried and loved, though I usually forget until the sauce is already made.

Serving Suggestions

This casserole is rich, so I always serve it with something crisp and acidic to balance it out. A simple green salad with a sharp vinaigrette is perfect, or roasted asparagus if you're feeling fancy. A glass of chilled Chardonnay doesn't hurt either, though I've also served it with sparkling water and lemon when it's a weekday brunch.

• Pair it with a arugula salad dressed in lemon and olive oil.
• Serve it alongside roasted tomatoes for a pop of acidity.
• Offer fresh fruit or a berry compote to cut through the richness.

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This casserole has become my answer to lazy Sunday mornings and last-minute dinner guests alike. It's proof that comfort food doesn't have to be complicated, just generous and made with a little bit of care.

Recipe FAQs

→ Can I prepare this casserole ahead of time?

Yes, assemble the casserole up to 24 hours in advance, cover tightly, and refrigerate. Add 5-10 minutes to the baking time if baking directly from the refrigerator.

→ What cheese can I substitute for Gruyère?

Swiss cheese works beautifully as it has a similar melting quality and mild nutty flavor. Emmental or Comté are also excellent French alternatives.

→ How do I make this vegetarian?

Omit the ham and add sautéed mushrooms, caramelized onions, or fresh spinach between the bread layers for a flavorful meat-free version.

→ Why remove the bread crusts?

Removing crusts creates a more uniform texture and allows the bread to absorb the egg mixture and béchamel sauce more evenly, resulting in a softer, creamier casserole.

→ Can I freeze leftovers?

Yes, portion cooled casserole into airtight containers and freeze for up to 2 months. Reheat individual portions in the oven at 350°F until warmed through.

→ What bread works best for this dish?

White sandwich bread or brioche are ideal choices. Their soft texture soaks up the custard beautifully. Day-old bread actually works better as it absorbs liquid without falling apart.