Croque Monsieur Casserole

There was this tiny bistro near my old apartment in Paris that made the most incredible Croque Monsieur. I'd order it every Sunday, watching the cheese bubble through the window while steam curled up into the crisp morning air. When I moved back home, I spent months trying to recreate that magic in single sandwiches, but something was always slightly off. Then it hit me during a brunch gathering—I should make it as a casserole, letting all those flavors meld together in one gorgeous bubbling dish. The first time I served it, my friend actually closed her eyes and said she was back in that French corner booth.

Last winter, my sister came over during that bleak stretch where January feels like it will never end. We'd both had exhausting weeks, the kind where you just want someone else to handle dinner. I pulled this casserole out of the oven, the smell of Gruyère and nutmeg filling the whole kitchen. We stood there eating it straight from the dish with forks while watching snow fall outside, not saying much because comfort like that doesn't need conversation.

Ingredients

• 12 slices white sandwich bread: Remove the crusts for that uniform, elegant bistro look and let them dry slightly overnight for better absorption
• 2 tbsp unsalted butter: Softened to room temperature so it spreads easily without tearing the bread
• 1 1/2 cups Gruyère cheese: This nutty, complex French cheese is non-negotiable for authentic flavor, though Swiss works in a pinch
• 1 cup whole milk: Full fat is essential here—skim milk just won't give you that rich, custard-like texture
• 1/2 cup heavy cream: The secret ingredient that makes the bread pudding layer impossibly lush
• 3 large eggs: Room temperature eggs incorporate more smoothly into the milk mixture
• 8 slices cooked ham: Look for deli ham with some texture and natural smokiness
• 2 tbsp unsalted butter: For the béchamel sauce foundation
• 2 tbsp all-purpose flour: This will thicken your sauce perfectly without any lumps
• 1 1/4 cups whole milk: Cold milk prevents flour from clumping when you whisk it in
• 1/4 tsp ground nutmeg: Freshly grated if possible—it makes a surprising difference

Instructions

Preheat your oven:

Set it to 375°F and butter a 9x13 baking dish thoroughly, getting into all the corners

Make the béchamel:

Melt butter in a saucepan over medium heat, whisk in flour for 1 minute until it smells nutty, then gradually pour in milk while whisking constantly until smooth and thickened, about 3 to 4 minutes

Build your layers:

Butter one side of each bread slice, then arrange half butter-side down in the dish, followed by ham and Gruyère, then repeat with remaining bread, ham, and cheese

Whisk your custard:

Beat eggs with milk, cream, and a pinch of salt until combined, then pour slowly over the casserole, pressing down gently to help bread absorb every drop

Finish and bake:

Pour that velvety béchamel over the top, spread it to the edges, and bake for 35 to 40 minutes until puffed up like a golden, bubbling masterpiece

Save

My friend Sophie makes this every Christmas morning now, but she's added her own twist—she tucks thin slices of pear between the layers. That first sweet bite against all the savory richness absolutely changed how I think about this dish. Sometimes the best recipes are just starting points for something even better.

Making Ahead For Brunch

You can assemble this entire casserole the night before and refrigerate it uncovered overnight. The bread will soak up that custard even more deeply, creating an almost bread-pudding consistency that's absolutely incredible. Just add 5 to 10 minutes to the baking time since you're starting with a cold dish.

The Vegetarian Version

Swap the ham for thinly sliced portobello mushrooms that have been sautéed until golden and slightly crispy. You'll get that umami depth without the meat, and the earthiness plays beautifully with the nutmeg in the béchamel. Sometimes I'll add a handful of fresh spinach too for color.

Serving Suggestions

A crisp green salad with a sharp vinaigrette will cut through all that richness perfectly. I like to serve it with warm crusty bread for soaking up any extra sauce on the plate.

• Don't skip the Dijon mustard if you want that authentic bistro kick
• A glass of Chardonnay ties everything together elegantly
• Fresh thyme leaves sprinkled on top add a lovely herbal finish

Save

There's something deeply satisfying about taking a classic restaurant dish and making it even better at home. This casserole has fed me through broken hearts, celebrations, and endless Tuesday nights when only French comfort food would do.

Recipe FAQs

→ Can I prepare this casserole ahead of time?

Yes, you can assemble the entire casserole, excluding the baking step, and refrigerate it overnight. Allow it to come to room temperature for about 30 minutes before baking as directed.

→ What kind of cheese works best if I don't have Gruyère?

While Gruyère offers a distinctive nutty flavor, Swiss cheese is an excellent and common substitute. Emmental or even a sharp white cheddar could also work for a different flavor profile.

→ How can I make this dish vegetarian?

Simply omit the ham. For added flavor and substance, you can incorporate sautéed mushrooms, spinach, or even vegetarian 'ham' slices between the bread layers.

→ Can I freeze this casserole?

It's best enjoyed fresh, but you can freeze baked leftovers in an airtight container for up to 3 months. Thaw overnight in the refrigerator and reheat gently in the oven.

→ What accompaniments pair well with this rich casserole?

Serve it warm, perhaps with a light, crisp green salad dressed with vinaigrette to cut through the richness. A glass of dry white wine, like Chardonnay, also pairs wonderfully.