Croque Monsieur Casserole

My friend Sophie taught me this recipe after I confessed I'd never successfully flipped a croque monsieur without the cheese sliding everywhere. She laughed and said forget flipping, just layer everything in a dish and let the oven do the work. That Sunday morning, watching the casserole puff and turn golden while we drank coffee, I realized some of the best recipes are the ones that simplify without sacrificing a single bit of indulgence. The smell of nutmeg and melted Gruyère filled her tiny kitchen, and I've been making it this way ever since.

I made this for my parents' anniversary brunch, and my dad, who usually critiques everything, went silent after the first bite. My mom kept sneaking extra servings when she thought no one was looking. The casserole sat in the center of the table, still bubbling at the edges, and for a moment everyone just enjoyed the warmth and the way the ham and cheese stretched with every scoop. It became our new tradition after that, the dish we make when we want something special without the fuss.

Ingredients

• White sandwich bread: Removing the crusts helps the custard soak through evenly, and using sturdy white bread prevents sogginess while keeping that classic bistro texture.
• Unsalted butter: Buttering each slice before layering adds richness and helps the top crisp up beautifully in the oven.
• Gruyère cheese: This nutty, slightly sweet cheese melts like a dream and gives the casserole that authentic French flavor, though Swiss works in a pinch.
• Whole milk and heavy cream: The combination creates a luscious custard that binds everything together without being too heavy.
• Large eggs: They help the custard set and give the casserole structure so it slices neatly after resting.
• Cooked ham: Use good quality deli ham or leftover holiday ham for the best flavor and texture.
• All-purpose flour: The base of the béchamel, it thickens the sauce and creates that creamy top layer.
• Ground nutmeg: Just a pinch transforms the béchamel from plain white sauce to something warm and sophisticated.

Instructions

Prep the oven and dish:

Preheat to 375°F and butter your baking dish generously so nothing sticks. The butter also adds flavor to the edges as they bake.

Make the béchamel:

Melt butter, whisk in flour, and cook for a minute to remove the raw flour taste, then slowly add milk while whisking constantly until it thickens and coats the back of a spoon. Season with nutmeg, salt, and pepper, then set aside.

Butter and layer the bread:

Spread softened butter on one side of each slice, then arrange half the slices buttered side down in the dish. This creates a golden, crispy bottom layer.

Build the layers:

Add half the ham and half the Gruyère, then repeat with remaining bread, ham, and cheese, pressing gently as you go. The layers should feel snug but not crammed.

Pour the custard:

Whisk eggs, milk, cream, and a pinch of salt together, then pour evenly over the casserole and press down gently so the bread soaks it up. Let it sit for a minute if the bread seems dry.

Add béchamel and bake:

Spread the béchamel over the top in an even layer, then bake uncovered for 35 to 40 minutes until puffed, golden, and bubbling at the edges. Let it rest for 10 minutes so the custard sets and you can slice it cleanly.

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One winter evening, I brought this casserole to a potluck, and a quiet neighbor I'd never spoken to came back for seconds, then asked for the recipe. We ended up talking for an hour about cooking and Paris and how food always seems to open doors between strangers. She still emails me photos whenever she makes it, and every time I smile remembering how a simple casserole turned into an unexpected friendship.

Making It Your Own

If you want a vegetarian version, leave out the ham and add sautéed mushrooms or wilted spinach between the layers. I've also tucked in thin slices of tomato and fresh thyme, which brought a summery brightness to the dish. For extra depth, spread a thin layer of Dijon mustard on the bread before layering, it cuts through the richness and adds a sharp, tangy note that makes every bite more complex.

Serving Suggestions

This casserole shines at brunch alongside a crisp green salad with a lemony vinaigrette to balance the richness. I like to serve it with roasted asparagus or a simple arugula salad, and a glass of chilled Chardonnay or sparkling water with lemon. Leftovers reheat beautifully in the oven, and I've even packed cold squares for lunch the next day, which taste surprisingly good at room temperature.

Storage and Reheating

Store leftovers covered in the fridge for up to three days, and reheat individual portions in a 350°F oven for about 15 minutes until warmed through. You can also assemble the casserole the night before, cover it tightly, and refrigerate, then bake it fresh the next morning, just add an extra five minutes to the baking time. Freezing works too, wrap it well before baking and freeze for up to a month, then thaw overnight and bake as directed.

• Always let the casserole come to room temperature for 20 minutes before reheating so it warms evenly.
• Cover with foil if the top starts browning too quickly during reheating.
• Use a sharp knife to slice cleanly through the layers and serve on warm plates.

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This casserole has become my answer to lazy Sundays and last minute gatherings, proof that comfort food does not have to be complicated. I hope it fills your kitchen with the same warmth and easy joy it has brought to mine.

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. Pour the béchamel sauce on top just before baking, and add 5-10 minutes to the baking time if starting from cold.

→ What cheese can I use instead of Gruyère?

Swiss cheese is the closest substitute with a similar nutty flavor. Emmental, Comté, or a sharp white cheddar also work well. Avoid pre-shredded cheese for best melting results.

→ How do I make this vegetarian?

Omit the ham and add sautéed mushrooms, caramelized onions, or wilted spinach between the bread layers. The béchamel and cheese provide rich, satisfying flavor without meat.

→ Why remove the bread crusts?

Removing crusts helps the bread absorb the custard mixture more evenly and creates a softer, more uniform texture throughout the casserole. It also gives a more refined presentation.

→ Can I freeze leftovers?

Yes, cool completely, then wrap individual portions in foil and freeze for up to 2 months. Reheat in a 350°F oven until warmed through, about 20-25 minutes from frozen.

→ What should I serve alongside this dish?

A crisp green salad with a tangy vinaigrette balances the richness perfectly. Roasted asparagus, fresh fruit, or a simple arugula salad also pair beautifully.