Croque Monsieur Recipe-Make it, you won't be sorry!

Morgan found THIS recipe on Pinterest and it is awesome!   Next time we decided to make it a little differently though.  We got our croissants at Trader Joe's and they were so delicious but very hard to cut so we decided to break them up next time and make it a layered casserole instead.  We also halved the recipe. 
Madison and Morgan also had me add a fried egg to theirs and omited the mustard.  I kept the mustard and liked it.

Ingredients-

• 2 tablespoons unsalted butter
• 3 tablespoons all-purpose flour
• 2 cups hot milk
• 1 teaspoon kosher salt
• 1/2 teaspoon freshly ground black pepper
• Pinch nutmeg DIDNT USE THIS
• 12 ounces Gruyere, grated (5 cups) SUBBED TRADER JOES GRADED SWISS/GRUYERE MIX
• 1/2 cup freshly grated Parmesan
• 8 croissants
• Dijon
• 8 ounces honey ham, sliced but not paper thin SUBBED REGULAR HAM FOR HONEY

Preheat the oven to 400 degrees F.
Melt the butter over low heat in a small saucepan and add the flour all at once, stirring with a wooden spoon for 2 minutes. Slowly pour the hot milk into the butter–flour mixture and cook, whisking constantly, until the sauce is thickened. Off the heat add the salt, pepper, nutmeg, 1/2 cup grated Gruyere, and the Parmesan and set aside.
Halve and toast the croissants, place the slices on 2 baking sheets and bake for 4 minutes. Turn each slice and bake for another 2 minutes, until toasted.
Lightly brush half the croissant with mustard, add a slice of ham to each, and sprinkle with half the remaining Gruyere. Top with another piece of toasted bread. Slather the tops with the cheese sauce, sprinkle with the remaining Gruyere, and bake the sandwiches for 5 minutes. Turn on the broiler and broil for 3 to 5 minutes, or until the topping is bubbly and lightly browned. Serve hot.

Adapted from savuryandsweet adapted from Barefoot Contessa