Croque Monsieur Casserole

My tiny Paris apartment kitchen smelled like warm butter and melting Gruyère the first time I attempted this casserole adaptation of the classic bistro sandwich. I was hosting friends for brunch and had forgotten that making individual Croque Monsieurs for six people would take forever. The casserole was a desperate pivot that ended up becoming the most requested dish at every gathering. Something magical happens when the béchamel soaks into the bread and those Gruyère crusted edges emerge from the oven all golden and bubbling.

Last Christmas morning my sister walked into the kitchen while this was baking and actually teared up because the smell reminded her of our trip to France. We ended up eating it straight from the baking dish while still in pajamas, burning our mouths but unable to stop. The leftovers were nonexistent.

Ingredients

• 12 slices white sandwich bread: Removing the crusts helps the bread absorb the custard evenly without any tough edges
• 2 tbsp unsalted butter: Softened butter spreads more easily and coats each bread slice uniformly
• 1 1/2 cups Gruyère cheese: This Swiss style cheese melts beautifully and adds that signature nutty depth but Swiss works too
• 1 cup whole milk and 1/2 cup heavy cream: The combination creates the perfect rich custard without being overly heavy
• 3 large eggs: Room temperature eggs incorporate more smoothly into the milk mixture
• 8 slices cooked ham: Good quality deli ham makes a noticeable difference in flavor
• 2 tbsp butter and 2 tbsp flour: This classic roux ratio creates a silky béchamel that wont become gluey
• 1 1/4 cups whole milk: Warm the milk slightly before adding it to the roux to prevent lumps
• 1/4 tsp ground nutmeg: Just a pinch adds that traditional French café warmth

Instructions

Get your oven ready:

Preheat to 375°F and butter a 9x13 baking dish thoroughly because those cheese edges need room to bubble without sticking

Make the béchamel first:

Melt 2 tablespoons butter over medium heat, whisk in flour for exactly one minute to cook out the raw taste, then gradually whisk in 1 1/4 cups milk, stirring constantly until thickened and smooth

Layer like a pro:

Butter one side of each bread slice and arrange half buttered side down, add half the ham and cheese, repeat layers, then press gently so everything nests together

Create the custard:

Whisk eggs with 1 cup milk, cream, and a pinch of salt until completely combined, then pour evenly over the entire casserole

Add the crown:

Pour that beautiful béchamel sauce over the top and spread it into every corner so no dry bread remains exposed

Bake until golden:

Slide it into the oven for 35 to 40 minutes until puffed up and bubbling, then let it rest for 10 minutes because cutting too soon will spill all that creamy goodness

Save

This recipe has saved me more times than I can count when unexpected guests arrive or I need to feed a crowd on a budget. My neighbor started making it for Sunday supper and her family requests it weekly now.

Make It Your Own

Sometimes I swap turkey for ham or add sautéed mushrooms between layers for a vegetarian version. A thin layer of Dijon mustard on the bread adds just the right kick. The beauty is how adaptable it is while still feeling special.

Serving Suggestions

A crisp green salad with bright vinaigrette cuts through all that richness perfectly. I love serving this with a chilled glass of Chardonnay or a light French red. Fresh berries or a simple fruit salad finish the meal beautifully.

Timing Tips

The casserole needs those 10 minutes of resting time or it will be too loose to serve cleanly. I set the table while it rests so everything is ready when we sit down. Leftovers reheat surprisingly well in a low oven.

• Butter the baking dish really well including all the corners
• Grate your own cheese instead of buying pre shredded for better melting
• Let the béchamel cool slightly before pouring over the assembled layers

Save

There is something deeply satisfying about serving a dish that looks impressive but comes together with such simple ingredients. Every bite feels like a warm hug from a French grandmother you never knew you needed.

Recipe FAQs

→ Can I prepare this dish in advance?

Yes, you can assemble the entire casserole up to a day ahead. Cover it tightly and refrigerate. Let it come to room temperature for about 30 minutes before baking, or add an extra 10-15 minutes to the baking time if baking straight from the fridge.

→ What are good substitutions for Gruyère cheese?

While Gruyère offers a distinct nutty flavor, Swiss cheese is a great alternative. For a sharper taste, you could also use a combination of Emmental and a little Parmesan.

→ How can I make this vegetarian?

To make a vegetarian version, simply omit the ham. You can substitute it with sautéed mushrooms, spinach, or roasted red peppers to add more flavor and substance to the dish.

→ What should I serve alongside this casserole?

This rich casserole pairs wonderfully with a light and crisp green salad dressed with a vinaigrette to cut through the richness. A glass of dry white wine, like Chardonnay, also complements it beautifully.

→ How do I store and reheat leftovers?

Store any leftover casserole in an airtight container in the refrigerator for up to 3 days. To reheat, you can warm individual portions in the microwave or cover the dish with foil and bake in a preheated oven at 300°F (150°C) until heated through.