For years I’ve seen Croque-Monsieur on menus and thought, “hmmm, a grilled cheese made into French toast…” Thanks, but I think I’ll pass. Then, I had this version…with béchamel…mmmm. Croque-Monsieur is a knife and fork sandwich. You want good bread, cut not too thick. And good ham, and of course, cheese. I like a combo of Swiss and Gruyère. This is a great mid-week-supper-meal, because it can be made ahead. Make the Mornay ahead, cover with plastic wrap, directly on the sauce (this prevents a skin from forming) and have it chillin’ in the fridge. Assemble the sandwiches ahead and have them waiting in the fridge. Then, when you’re ready to serve, plop the Mornay on top, into a hot oven, a few moments under the broiler and it’s dinner!
So, what’s a Mornay sauce, you ask? It’s a béchamel sauce, with cheese added at the end. For this particular iteration, 
I like to sauté finely minced shallots in the butter. 
For the cheese, I like a combination of Gruyère and Swiss cheese. 
You want this to be about the consistency of mayonnaise, because that’s pretty much what we’re replacing with the sauce. The Mornay is used both inside and on the outside of the sandwich.
To assemble the sandwich, 
I prefer to use brioche bread, when possible, but any good, substantial bread will work well. I toast the bread ever-so lightly. This gives the sandwich better texture. I place half the toasted bread slices on a foil-lined sheet pan. Smear with about 1 1/2-2 tablespoons of the Mornay sauce. 
I add slices of Swiss cheese. For the ham, you want to use good, flavorful ham. I like a ham that’s a bit on the sweet side. 
As you know, The Goddess lives for onions, so she adds some shaved red onion slices. This is not traditional, but it is truly delicious. Also, feel free to add a smear of Dijon mustard. 
Put the sandwiches together. If you’re making the sandwiches ahead to serve later, this is your stopping point. Now to finish, smear a good thick layer of Mornay over the top, pushing the sauce completely to the edge. (you can see I didn’t do that well enough…next time. Life is a learning curve.) 
I sprinkle extra shredded Swiss/Gruyère on each sandwich. 
Slide the pan into the oven for a few minutes, about 5-10 minutes. You’ll use the longer amount of time, if the sandwiches were refrigerated. I slide the pan under the broiler, for a short time. 
It helps them become all melty, bubbly and browned. And now to the table….
In the interest of research, I tried using crab meat instead of the ham. It was very tasty, but I really think the ham was better. But, that could just be my personal taste buds, so you should try other options yourself. If you use gluten-free bread, and rice flour to thicken the béchamel, then our gluten-intolerant friends can enjoy this delight.
Croque-Monsieur with Mornay Sauce
- Mornay Sauce:
- 1/2 stick unsalted butter
- 3 tablespoons very finely minced shallots (or onions)
- 1/4 cup flour or 3 tablespoons rice flour
- 1 cups whole milk
- 1/2 cup half-and-half
- 1 tablespoon Dijon mustard
- 1-2 teaspoons lemon juice
- 3/4 cup shredded Gruyère (about 2 ounces)
- 1/4 cup finely shredded Parmesan-Reggiano
- 1/4 teaspoon freshly grated nutmeg
- Kosher salt
- Sandwiches:
- 8 slices 1/2-inch-thick country-style or brioche bread
- 8 slices good ham (I like a slightly sweet ham)
- 4-8 slices Gruyère or Swiss cheese
- Dijon mustard
- Very thinly sliced red onions (optional)
- 6 tablespoons shredded Gruyère, for topping the sandwiches
To make the Mornay: Melt butter in a medium saucepan over medium heat until foamy. Add the shallots; continue to cook until the shallots begin to wilt, about 2 minutes. Whisk in the flour; cook, whisking, until mixture is pale and foamy, about 2-3 minutes. Gradually add milk, whisking until mixture is smooth. Add the lemon juice and continue to cook, whisking, until sauce is thick and somewhat elastic, about 3 minutes. Remove from heat. Whisk in mustard, nutmeg and cheeses; season with salt.
Make ahead: The Mornay can be made 1 day ahead. Let cool; press plastic wrap directly onto surface and chill.
Preheat oven to 425°. Very lightly toast the bread. Spread 4 bread slices with a skim of mustard. Spread 2 tablespoons béchamel, evenly over each of the 4 slices of toasted bread, extending all the way to the edges. Place these 4 slices of bread, béchamel side up, on a parchment-lined baking sheet; top with ham, cheese slices and onion slices, if using. Top with remaining slices of bread. Spread the remaining Mornay (evenly divided) over each of the four sandwiches, spreading completely to the edges. Sprinkle evenly with the shredded cheese. Bake until warmed through the cheese begins to brown, about 5-8 minutes. Turn the broiler to HIGH and broil until nicely browned, 1-2 minutes.
Make ahead: Sandwiches can be completely assembled 1 day ahead. Cover; chill. Then bake and broil as directed.
NOTE: If you make these ahead, I usually don’t top the sandwiches with the Mornay, until just before I put them in the oven.
Croque-Monsieur with Mornay Sauce Recipe©Marcia Lahens 2017. All rights reserved.
The last time I made these, I added some thin slices of beefsteak tomatoes to each sandwich. They were delicious, but it does make the sandwich “juicier”.
Goddess Cooks 