Croque Monsieur Casserole

The smell of nutmeg in béchamel always takes me straight back to a chilly Sunday morning when I needed to feed eight people with what was left in the fridge. I had bread going stale, a wedge of Gruyère, and deli ham that needed using. Instead of making individual sandwiches, I piled everything into a baking dish, whisked together a custard, and hoped for the best. What came out of the oven was golden, bubbling, and gone in minutes.

I made this for my neighbors during a snowstorm, and they still bring it up every winter. We sat around the table with seconds and thirds, the casserole sitting in the middle like the star of the show. The creamy béchamel pooled around the edges, and everyone scraped their plates clean. It was one of those meals where no one wanted to leave the table.

Ingredients

• White sandwich bread: Use soft, slightly stale bread if you have it, as it soaks up the custard without turning to mush, and always remove the crusts for that classic tender bite.
• Gruyère cheese: This nutty, melty cheese is what makes the dish taste authentically French, though Swiss works in a pinch if thats what you have on hand.
• Cooked ham: Deli ham works perfectly here, just make sure its not too salty or it will overpower the creamy layers.
• Whole milk and heavy cream: The combination creates a rich custard that binds everything together and keeps the casserole from drying out.
• Eggs: They turn the milk mixture into a custardy base that puffs up beautifully in the oven.
• Béchamel sauce: Made with butter, flour, milk, and nutmeg, this is the secret layer that makes it taste like a bistro splurge.

Instructions

Get the oven ready:

Preheat your oven to 375°F and butter a 9x13-inch baking dish generously so nothing sticks. This step seems small, but it makes cleanup so much easier later.

Make the béchamel:

Melt butter in a saucepan, whisk in flour, and let it bubble for a minute before slowly adding milk, whisking constantly until it thickens into a smooth, velvety sauce. Season it with nutmeg, salt, and pepper, then set it aside while you build the layers.

Butter the bread:

Spread softened butter on one side of each slice, then lay half of them buttered side down in the dish. The butter creates little pockets of richness that make every bite better.

Layer the ham and cheese:

Add half the ham slices and half the grated Gruyère, then repeat with the remaining bread, ham, and cheese. Press down gently 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 the bread down so it soaks up the liquid. Let it sit for a minute or two if you have time.

Add the béchamel and bake:

Spread the béchamel sauce over the top and slide the dish into the oven for 35 to 40 minutes, until its puffed, golden, and bubbling at the edges. Let it rest for 10 minutes before cutting into it, or youll have a beautiful mess on your hands.

Save

This casserole became my go-to whenever I wanted to feel like I had my act together without actually spending hours in the kitchen. Its the kind of dish that makes people think you went to culinary school, when really you just layered things and let the oven do the work. I love how it fills the house with that warm, cheesy, toasty smell that makes everyone wander into the kitchen asking whats for dinner.

How to Make It Ahead

You can assemble the entire casserole the night before, cover it tightly with plastic wrap, and keep it in the fridge until youre ready to bake. Just let it sit at room temperature for about 20 minutes before it goes into the oven, and add an extra 5 minutes to the baking time if its still cold. This trick has saved me on busy mornings more times than I can count.

What to Serve It With

A crisp green salad with a sharp vinaigrette cuts through the richness perfectly, and a glass of chilled Chardonnay or sparkling water with lemon feels just right. I also love serving it with a bowl of fresh fruit on the side, especially during brunch when you want something light to balance all that cheese and cream. Sometimes I put out cornichons and whole grain mustard for people who want a little tangy contrast.

Ways to Switch It Up

If you want to make it vegetarian, skip the ham and add sautéed mushrooms, spinach, or roasted tomatoes between the layers. You can also brush Dijon mustard on the bread before layering for a sharper, more classic croque monsieur flavor. I once added caramelized onions and it turned into something even more indulgent.

• Try using sourdough or brioche instead of white bread for a richer, more textured base.
• Swap Gruyère for Comté or Emmental if you want a slightly different flavor profile.
• Add a handful of fresh thyme leaves to the custard for an herby, earthy twist.

Save

This casserole has become one of those recipes I make without thinking, the kind that feels like a warm hug on a plate. I hope it brings as much comfort to your table as it has to mine.

Recipe FAQs

→ Can I make this casserole ahead of time?

Yes, assemble the casserole up to 24 hours in advance. Cover tightly and refrigerate, then add 10 minutes to the baking time if baking directly from cold.

→ What cheese can I use instead of Gruyère?

Swiss cheese is the closest substitute, but Comté, Emmental, or even sharp white cheddar work well. Each brings a slightly different flavor profile to the dish.

→ How do I prevent the casserole from becoming soggy?

Use day-old bread or lightly toast the slices before assembling. This helps the bread hold its structure while absorbing the custard and béchamel without becoming mushy.

→ Can I freeze leftovers?

Yes, portion the 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 should I serve alongside this casserole?

A crisp green salad with Dijon vinaigrette balances the richness perfectly. Roasted asparagus or a simple arugula salad with lemon also complement the flavors beautifully.

→ How can I make this vegetarian?

Omit the ham and add sautéed mushrooms, caramelized onions, or wilted spinach between the bread layers. You can also use vegetarian ham alternatives available in most grocery stores.