01 -
Melt the butter first, then mix in cornstarch, pepper, and salt until it bubbles. Pour milk in three parts, letting it thicken between each addition.
02 -
Smear butter on the outside of each bread slice. Add Dijon on the inside, then put ham and cheese between slices.
03 -
Put sandwiches in a pan or griddle and cook until they're golden brown and the cheese starts melting.
04 -
Pour white sauce over sandwiches and sprinkle with shredded cheese. Place under broiler until bubbly and browned.