We had our hands full with creating an at-home version of this French, not-your-average grilled cheese sandwich—from trying to figure out the right consistency for the Mornay (cheese sauce) to making sure that there weren't any exposed bits of bread that would dry out and burn after broiling the sandwich. But in the test kitchen, we're always up for a cheesy challenge. See the steps we took to perfect this recipe.
We Take Grilled Cheese to New Heights with Our Croque Monsieur Recipe
To define the croque monsieur (loosely translated from French as “Mr. Crunch”) as a grilled ham-and-cheese sandwich is to vastly understate it. This big bistro favorite—two slices of butter-brushed bread toasted up crisp and layered with sweet, salty ham; creamy white sauce; and plenty of nutty Gruyère cheese—is beautiful to behold and so rich, runny, and substantial that it requires a fork and knife to eat.
The traditional method calls for griddling the sandwiches individually, topping them with cheese, and then sliding them under a broiler to finish, but we wanted four sandwiches all at once. And we wanted to keep the crunch in the croque and not allow the sauce to turn everything soggy.
All good sandwiches start with good bread, and after auditioning baguette, sourdough, and others, we chose eight slices of white sandwich bread, which stayed tender while also taking on plenty of crunch. After brushing each slice evenly on both sides with melted butter, we lined them up on an oiled baking sheet and slipped them into the oven to toast.
Most recipes for croque monsieur call for a simple white sauce (a béchamel, which is common in many macaroni and cheese recipes) as well as grated Gruyère. (Read “Does Milk Temperature Matter When Making a White Sauce or Béchamel?" to see if scalding the milk is necessary before adding it to the roux in step 3 of this recipe.) To simplify things, we decided to combine the two into a cheesy sauce (adding cheese to a béchamel turns it into a Mornay sauce). Getting the perfect ratio of ingredients for a spreadable but not runny consistency took some testing, but after a few rounds, the best formula revealed itself: 2 tablespoons each of flour and butter, cooked together briefly, and then 1 cup of whole milk stirred in along with 1¼ cups of shredded and grated cheeses—Gruyère, of course, plus a bit of Parmesan to add even more savoriness. A pinch of nutmeg (a classic addition) lent a mysterious warmth and complexity.
Choosing the ham was an easy task. Black Forest ham sliced to order (very thin) from the deli is tender, flavorful, and miles ahead of the presliced, packaged ham rectangles you get from the supermarket cooler. Delicately folding the ham over itself before laying it on the sandwich, rather than simply stacking it in flat sheets, made the sandwich easier to eat; no big sheets of ham came sliding out when we took a bite.
A bit more cheese sauce spread over the top of this sandwich and a final sprinkling of Parmesan and Gruyère before a trip under the broiler to meld it all together created a gorgeous, bubbly-browned top. (Read “Broiler Heat” to find out how much heat your broiler gives off. If it runs hot or cool you may need to adjust cooking times.) The result was a sandwich worth savoring with a knife and fork: grand, satisfying, and worthy of the title “monsieur.”