01 -
Set your oven to 400°F (200°C) to preheat.
02 -
Butter each slice, then toast both sides for 2 minutes.
03 -
Spread mustard on bread, layer on cheese, ham, another cheese slice, and cover with bread.
04 -
Place sandwiches on a baking tray after cutting each into 4 smaller squares.
05 -
Make a bechamel by melting butter, mixing in flour until golden, and slowly stirring in milk until it thickens.
06 -
Add Parmesan and season the sauce with salt and pepper.
07 -
Pour sauce over the sandwiches, bake for 6 minutes and then broil for 4 minutes until golden brown.