Ham and cheese is a classic sandwich combination. We give this panini a slight French flair by adding Dijon mustard and cheese sauce (Mornay), which melt into a perfectly oozy filling.
To make the sauce: Melt the butter in a saucepan set over medium-high heat.
Add the flour, stirring to incorporate. Slowly pour in the milk, stirring constantly, until a thick sauce forms.
Bring to a gentle simmer then add the cheese, stirring until it melts.
To make the sandwiches: Spread the warm sauce on one side of half the bread slices.
Top the sauce with a slice of ham, then a slice of cheese.
Spread the Dijon mustard on one side of the remaining slices of bread, and place them mustard-side-down onto the cheese.
Heat an electric panini griddle or skillet over medium-high heat.
Spread the top of the sandwich with butter, and place it butter-side down onto the hot surface.
Spread butter on the other side of the bread, then close the griddle or cover the pan with a lid.
Toast the sandwich for 3 to 5 minutes on one side, flip it over, and toast for another 3 to 5 minutes until it's as golden as you like. Remove from the pan, and serve warm.
To make French-inspired traditional croque monsieur sandwiches: Begin with 16 to 18 slices of soft white sandwich bread (we like pain de mie for its ideal size and shape), and prepare the sandwiches according to the recipe instructions. Heat an electric griddle or skillet over medium-high heat or preheat a waffle maker. Cook sandwiches according to recipe instructions. Keep the finished sandwiches in a warm oven while you prepare the remaining sandwiches.
