01 -
Heat oven to 400°F (200°C).
02 -
Brush bread slices with melted butter and toast each side for 2 minutes.
03 -
Layer mustard, cheese, ham, more cheese on bread slices and top with remaining bread.
04 -
Cut each sandwich into 4 mini squares and arrange on baking sheet.
05 -
Make béchamel sauce by melting butter, whisking in flour until golden, then gradually adding milk and cooking until thick.
06 -
Stir in Parmesan cheese and season with salt and pepper.
07 -
Spoon sauce over sandwiches, bake 6 minutes, then broil 4 minutes until golden.