Croque Monsieur breakfast casserole combines slices of baguette layered with good-quality ham and a light smear of Dijon mustard, finished with a creamy béchamel (mornay) sauce and melted Gruyère for a gooey center and golden, crispy edges. It’s ideal for holiday mornings and brunch gatherings because you can assemble it the night before and bake the next morning.
This recipe is a casserole interpretation of the classic French Croque Monsieur sandwich. It gives you all the familiar flavors—tangy Dijon, savory ham, and a rich cheese sauce—while filling a dish that serves a crowd. The baguette’s crisp crust and chewy crumb are essential: they toast up beautifully and help the casserole maintain texture instead of turning soggy.
Croque Monsieur breakfast casserole ingredients
- Baguettes: Use a crusty baguette so the exterior crisps and the interior gets a luscious custardy texture.
- Gruyère cheese: A melting Swiss cheese with a nutty flavor that complements the béchamel.
- Thinly sliced ham: Choose ham with good texture and flavor; avoid overly processed deli slices when possible.
- Eggs and half & half: These form the custard that binds the casserole and gives a French toast–like richness in the center.
- Béchamel (mornay) sauce: A simple roux-based sauce made from butter, flour and milk, finished with some grated Gruyère to make a cheese sauce.
- Dijon mustard: Adds bright acidity and a peppery bite to cut through the richness.
Specific ingredient amounts and full recipe measurements are included in the recipe card below.
How to make croque monsieur breakfast casserole
Step 1: Dry the bread and grate the cheese
Preheat the oven to 300°F. Cut baguettes into ½-inch slices and arrange on two sheet pans. Toast in the oven for 10–15 minutes, flipping occasionally, until the slices are dry and just lightly toasted. This helps the bread absorb the custard without becoming mushy.
Grate the Gruyère on a box grater or with a food processor and set aside. Freshly grated cheese melts more smoothly than pre-shredded varieties that contain anti-caking agents.
Chef’s tip: Grate your own cheese
Grating Gruyère yourself gives a creamier melt and better texture. Pre-shredded cheese often contains additives that can make the finished dish grainy.
Step 2: Layer the casserole
Increase the oven temperature to 350°F. Lay about half of the toasted baguette slices in the bottom of a 9 x 13-inch casserole dish, fitting them together as snugly and level as possible. Spread Dijon on the remaining slices, then arrange them in a shingled pattern over the base layer.
Pull the ham into small pieces and tuck one piece between each slice of bread so every bite has ham evenly distributed.
Step 3: Make the custard
Whisk together 4 eggs, 2 cups half & half and ½ teaspoon kosher salt in a large bowl. Pour the custard evenly over the layered bread, pressing gently so the slices absorb liquid. Refrigerate for 30 minutes while you prepare the béchamel. To make ahead, cover and refrigerate overnight after pouring the custard.
Step 4: Make the béchamel (mornay) sauce
Melt 2 tablespoons butter in a small saucepan over medium heat. Whisk in 2 tablespoons flour and cook about one minute.
Gradually whisk in 1 cup whole milk and keep the heat at medium. Whisk almost constantly until the sauce reduces by about one-third and thickens to coat the back of a spoon. Remove from heat and stir in ⅓ cup grated Gruyère and ¼ teaspoon kosher salt. Taste and adjust seasoning if needed.
Step 5: Top with sauce, cheese and bake
Pour the warm béchamel over the chilled casserole, leaving a few spots of exposed crust so you get crisp edges. Sprinkle the remaining ⅔ cup grated Gruyère evenly over the top.
Bake at 350°F for 35–40 minutes, until the cheese is bubbly and lightly browned. For a deeper golden top, switch the oven to broil for a minute or two—watch closely, as broilers can brown quickly. Let the casserole rest 5–10 minutes before serving.
Why baguettes work best
I tested this casserole with several bread types and found the baguette delivers the best texture and flavor. The crust provides contrast and prevents the center from becoming soggy, while the open crumb absorbs the custard for a tender, custardy interior. Skipping the mustard or using a soft sandwich loaf loses some of the Croque Monsieur character, so a baguette is worth the extra step.
More brunch recipes
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Zucchini Frittata
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Ukrainian Potato Pancakes (Deruny)
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Glazed Lemon Blueberry Scones
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Shakshuka with Feta
Recipe highlights
- All the signature Croque Monsieur flavors in a shareable casserole.
- Baguette slices provide a crisp top and custardy interior for ideal texture.
- Make-ahead friendly: assemble the night before and bake the next morning.
- Extra cheese in the béchamel plus a cheese topping makes this deeply satisfying.
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Recipe
Cheesy Croque Monsieur Breakfast Casserole
Ingredients
- 2 baguettes
- 1 cup grated Gruyère, divided
- 3 tablespoons Dijon mustard (approximately)
- 6 ounces thinly sliced ham
- 4 eggs
- 2 cups half & half
- ½ teaspoon kosher salt
For the béchamel
- 2 tablespoons unsalted butter
- 2 tablespoons flour
- 1 cup whole milk
- ¼ teaspoon kosher salt
Instructions
- Preheat oven to 300°F. Slice baguettes into ½-inch rounds and place on sheet pans. Toast 10–15 minutes until dry and lightly golden.
- Grate Gruyère and set aside.
- Increase oven to 350°F. Arrange half the baguette slices in a 9 x 13-inch casserole dish in a single layer.
- Spread Dijon on the remaining slices and arrange them in rows on top of the base layer. Tuck small pieces of ham between slices so the filling is even.
- Whisk eggs, half & half and ½ teaspoon kosher salt. Pour the custard over the bread and refrigerate 30 minutes (or cover and refrigerate overnight).
- Make the béchamel: melt butter in a saucepan over medium heat, whisk in flour and cook 1 minute. Gradually whisk in milk and simmer until sauce thickens and reduces by about one-third. Remove from heat and stir in ⅓ cup Gruyère and ¼ teaspoon kosher salt.
- Remove casserole from fridge, pour the béchamel over the top leaving some crust exposed for crispiness, and sprinkle remaining ⅔ cup Gruyère over the surface.
- Bake 35–40 minutes until cheese bubbles and begins to brown. Briefly broil if desired for a deeper golden top—watch closely. Let rest 5–10 minutes before serving.
Notes
- Baguette matters: The crust provides texture and prevents the center from becoming soggy while delivering the classic Croque experience.
- Broil with care: Broilers can brown quickly—do not leave the oven unattended when broiling the top.
- Make ahead: Béchamel can be made up to one week ahead; store airtight. The casserole can be assembled the night before; pour sauce and top with remaining cheese before baking.
Nutrition (per serving, estimate)
- Calories: 446 kcal
- Carbohydrates: 36 g
- Protein: 22 g
- Fat: 24 g
- Sodium: 1116 mg
Nutrition information is an estimate and not guaranteed to be exact.