01 -
Set your oven to 400°F (200°C) and let it warm up.
02 -
Toast both sides of the buttered bread until golden—around 2 minutes each.
03 -
Start layering: mustard, cheese slices, ham, a second layer of cheese, and then another slice of bread on top.
04 -
Slice sandwiches into 4 smaller pieces and place them evenly on a baking tray.
05 -
In a pan, whisk melted butter with flour. Let it cook until light brown, then slowly pour in milk while stirring. Heat until thickened.
06 -
Mix Parmesan into the sauce and season with salt and pepper to enhance the flavor.
07 -
Pour the sauce over the sandwiches. Bake for 6 minutes, then broil for an extra 4 minutes to crisp the top until golden brown.