Slowly pour the milk into the pot and cook, whisking, until the sauce is thickened.
Heat broiler to high with the rack 6 inches from the flame.
Place the bread on a baking sheet.
Photo: Marcus Nilsson
Lightly brush half the bread with mustard and layer on the ham.
Spoon the cheese sauce over the bread and sprinkle with the Parmesan.
Broil until the sauce is bubbly and lightly browned, 2 to 3 minutes.
2,000 calories a day is used for general nutrition advice.
