Name: Baked Croque Monsieur: The Ultimate French Gratinated Sandwich
Prep time: 15 min
Cook time: 30 min
Total time: 45 min
Yield: 4 servings
Cuisine: France
Ingredients: 250 ml whole milk; 30 g unsalted butter; 30 g all-purpose flour; 300 g grated gruyère cheese; 8 slices soft white sandwich bread; 8 slices quality cooked ham; Nutmeg, salt, and black pepper to taste; 1 tablespoon Dijon mustard

Croque Monsieur Gratinado: El Sándwich Gratinado Francés Definitivo

The croque monsieur is a beloved French bistro classic that originated in early 20th-century Paris. This gratinated version elevates the traditional sandwich by adding a silky béchamel sauce and a generous cheese topping that browns perfectly in the oven. It is ideal for a quick yet gourmet meal.

Ingredients

How many are you cooking for?

Original recipe for 4 servings

250 ml whole milk
30 g unsalted butter
30 g all-purpose flour
300 g grated gruyère cheese
8 slices soft white sandwich bread
8 slices quality cooked ham
Nutmeg, salt, and black pepper to taste
1 tablespoon Dijon mustard

Step by step

Follow the timeline: technique icon, time and temperature when relevant.

Step 1 Cook 5 min

Warm the milk in a non-stick saucepan over medium-low heat. Remove from heat and whisk in the butter and flour until completely smooth. This trick prevents lumps from forming in the base sauce.
Step 2 Pot / simmer 5 min

Return the saucepan to low heat and cook the béchamel for five minutes, stirring constantly with a silicone spatula. The sauce will thicken gradually; remove it as soon as it bubbles gently to avoid overcooking.
Step 3 Mix

Season the béchamel with nutmeg, salt, and freshly ground black pepper. Reserve a quarter cup for the final gratin and mix the rest with half the grated gruyère. Nutmeg enhances the dairy flavor without overpowering it.
Step 4 Prep

Generously spread one side of each bread slice with Dijon mustard. Place a slice of cooked ham on the un-spread slices and distribute the creamy béchamel on top. The mustard adds acidity that balances the richness of the cheese.
Step 5 Assemble

Top with the second bread slice and pour the remaining sauce over each sandwich. Evenly sprinkle the remaining gruyère to create a golden crust. Ensure the cheese layer is thick enough to prevent the bread from burning.
Step 6 Oven 20 min 180 °C

Preheat the oven to 180 °C using the fan setting. Place the trays on the middle rack and bake for twenty minutes. Circulating heat guarantees even browning without needing to turn the pieces.
Step 7 Serve 3 min

Remove from the oven and let the sandwiches rest for three minutes before serving. Resting allows the béchamel to settle and the melted cheese to reach the perfect texture. Serve immediately with a light green salad.

Storage

Store unbaked sandwiches in the fridge up to 24 hours wrapped in plastic wrap. Once baked, keep in an airtight container and reheat in a toaster or microwave to restore crispiness.

Chef tips

Use thin-crumb sandwich bread and lightly toast it so it absorbs the béchamel without falling apart.
Do not salt the milk at the start; add salt only at the end of the béchamel cooking to prevent curdling.
If the gratin browns too quickly, cover with foil during the last five minutes of baking.

Allergens

Gluten
Dairy

Diet

Not vegetarian (contains animal products)

This recipe contains cooked ham and is not suitable for vegetarians.

Variations

Substitutions for a vegan version

Instead of: 250 ml whole milk

Use: same amount of unsweetened oat milk (or soy for béchamel)

Why: Milk adds liquid, fat and dairy sweetness; plant milk keeps texture without casein.

Tip: Choose oat for creams and soy for binding sauces. Heat gently—do not boil hard or it may split.
Instead of: 30 g unsalted butter

Use: same amount of extra virgin olive oil or plant-based margarine

Why: Butter provides fat and dairy flavour; oil or vegan margarine cover the fat without animal products.

Tip: In baking use cold margarine cubes. In pans, olive oil over medium heat—do not burn.
Instead of: 300 g grated gruyère cheese

Use: same amount of grated vegan cheese or mix 2 parts nutritional yeast + 1 part ground almonds

Why: Cheese adds fat, salt and umami; nutritional yeast mimics fermented flavour in sauces and gratins.

Tip: Add off heat to melt. For gratin, use vegan cheese that melts well. Taste for salt before serving.
Instead of: 8 slices quality cooked ham

Use: same amount of seitan strips, cooked brown lentils or sliced portobello mushrooms

Why: Meat provides chewable protein and fat; you need a substitute that survives long cooking and absorbs spices.

Tip: If using lentils, keep them whole for texture. With seitan, sear over high heat first. Adjust salt at the end.

Other variations

Swap the ham for garlic and thyme sautéed mushrooms for a meat-free version that keeps the umami texture.
Add thin slices of green apple and a splash of dry cider to the béchamel for a sharp, autumnal contrast.

Quick summary

At-a-glance while you cook. Full details are in the step-by-step.

1 Thicken warm milk with butter and flour over medium heat, stirring constantly until smooth and creamy in five minutes.
2 Spread Dijon mustard on bread slices and layer cooked ham evenly on half to build the sandwich base.
3 Cover the ham with creamy béchamel and a generous layer of grated gruyère before adding the top bread slice.
4 Pour remaining sauce over each sandwich and sprinkle extra cheese to guarantee a golden, crispy baked crust.
5 Bake at 180 °C for twenty minutes until the surface bubbles and turns a deep, uniform golden brown.
6 Rest for three minutes before serving so the sauce sets and the melted cheese achieves the perfect texture.