Preheat oven to 350°, you'll want that ready to go.
Mornay Sauce
In a sauce pan over medium heat, melt butter, then sprinkle in flour. Whisk that together and keep whisking until foaming. Slowly pour in your whole milk, then the salt, pepper, and nutmeg (optional). Whisk your sauce until bubbly and thick. Whisk in shredded gruyere cheese. Once fully incorporated and smooth, remove sauce from heat.
2 Tbsp butter, 2 Tbsp all-purpose flour, 2 cup whole milk, warmed*, 1 tsp ground nutmeg, 1 cup gruyere cheese, shredded, dash salt and pepper
Building Your Sandwich
For Toasted Bread: Place your oven safe pan over medium heat. Spread each slice with soft butter and toast the buttered bread (butter side down) in your pan. Then turn heat off while making sandwiches. On non-buttered side of bread: spread Dijon mustard, Mornay Sauce, 3 slices of ham, a handful of shredded gruyere, and top with another slide of bread. Spread a little more Mornay Sauce on top of the bread and finish with more gruyere cheese.
For Non-Toasted Bread: In an oven safe pan, butter one side of your bread, place slices of bread (butter side down) into the pan. On non-buttered side of bread: spread Dijon mustard, Mornay Sauce, 3 slices of ham, a handful of shredded gruyere, and top with another slide of bread. Spread a little more Mornay Sauce on top of the bread and finish with more gruyere cheese.
Bake your sandwiches for 15-18 minutes. Watch for burnt edges (which I happen to like, but it's up to you).
Croque Madame
Fry your egg how you like it, season with salt and pepper, then place one egg on top of your sandwich. Enjoy!
4 large eggs, butter for frying, salt and pepper
Notes
*By warming your milk a little, you can cut down the whisking time making your sauce. You can substitute a lower fat milk option, but your sauce may be thinner in the end.This is a mashup of 2 different Croque Madame recipes. The nutmeg is an optional ingredient, but I highly recommend trying it with first.This recipe can be for both Croque Madame and Croque Monsieur. Croque Madame has the egg on top. Leave it off for Croque Monsieur.We buy our gruyere cheese at Costco. It's the most economical option available for us.