Sep 12th 2026

Croque-Monsieur with Mornay Sauce

French Comfort Food

Croque-Monsieur with Mornay Sauce

A grilled ham and cheese sandwich, if the grilled ham and cheese sandwich had gone to culinary school. Fifteen minutes of work, fifteen more in the oven.

A croque-monsieur looks like a fancy grilled cheese and gets treated like one, which is a shame. The whole point of it is the Mornay sauce, a béchamel with cheese melted in, poured over the top before it goes in the oven.

Take that step out and you just have a hot ham sandwich. Put it in and you have something that shows up on café menus in Paris for a reason.

This one takes about half an hour, most of it hands-off in the oven.

What Actually Makes It a Croque-Monsieur

Ham and cheese between two slices of bread is a sandwich in every country. What makes this French is the sauce and the oven. No ham and cheese sandwich in America gets baked under a blanket of Mornay until it’s bubbling and colored on top.

Add a fried egg on top and it becomes a croque-madame. Same sandwich, different hat.

A good croque-monsieur is judged the same way a good grilled cheese is: by the color on top and the pull when you cut into it.

The Recipe

Serves 2. Prep: 15 min. Cook: 15 min.

You’ll Need

A saucepan, a whisk or spatula, and a baking sheet lined with parchment paper.

For the Mornay Sauce

  • 2 Tbsp butter
  • 2 Tbsp flour
  • 1 cup milk, cold
  • 2 pinches salt
  • 1 pinch pepper
  • 1 pinch nutmeg
  • 1 Tbsp truffle oil (optional)

For the Sandwich

  • 4 slices country sourdough bread (or sandwich bread)
  • 4 slices ham, prosciutto, or country ham
  • ½ cup grated Swiss cheese
  • ½ cup grated Parmesan
  1. Preheat. Set the oven to 450°F.
  2. Start the roux. Melt the butter in a saucepan, add the flour, and stir with a spatula. Cook a few minutes over low heat, without letting it brown.
  3. Build the sauce. Over medium heat, gradually whisk in the cold milk. Let it boil about 5 minutes until it thickens. Stir in salt, pepper, nutmeg, truffle oil if using, and half of the cheeses.
  4. Assemble. Spread a thin layer of Mornay on a slice of bread. Layer cheese, ham, more cheese, and a second slice of ham. Top with the second slice of bread.
  5. Top it off. Spread the remaining Mornay over the top slice and sprinkle with the rest of the shredded cheese.
  6. Bake. Place on a parchment-lined baking sheet and bake 10–15 minutes, until deeply colored and crisp on top. Serve warm.

The French Way of Doing It

Don’t skip the second layer of Mornay on top. That’s what browns and blisters in the oven. Without it, you just have a baked sandwich.

Let it rest a minute before cutting. Straight from the oven, the sauce is molten and it will run everywhere the second you cut in.

Want to Get This Right, Hands-On?

A good Mornay comes down to timing and a bit of muscle memory. It’s exactly the kind of technique I walk through in our cooking classes — the sauce, the roux, and a few other basics that make everything after this easier.

See Our Cooking Classes

If you want to go deeper on the condiment that pairs best with this, our guide to Dijon mustard is worth a read, a thin layer inside the sandwich changes the whole thing.