Make the béchamel: melt the butter in a small pan, add the flour and cook for 1 minute, stirring, so it loses its raw taste without browning.
Stirring constantly, gradually pour in the cold milk and cook for 3-4 minutes until it becomes a thick, creamy sauce. Season with salt, white pepper and nutmeg, and stir in a quarter of the cheese.
Preheat the oven to 200 °C (grill setting).
Butter the outsides of the bread thinly. Spread the insides of two slices with a little béchamel (and mustard), add the ham and a quarter of the cheese, then cover with the other two slices, buttered side out.
Toast the sandwiches in a frying pan over medium heat for 2 minutes per side until golden.
Put them on a baking tray, spread the tops thickly with the rest of the béchamel and sprinkle with the rest of the cheese.
Grill at the top of the oven for 5-7 minutes until the cheese melts, bubbles and browns in patches. Serve at once, hot.
A Receptnaptár original recipe. Calories and protein are estimated.