Method:

To make the béchamel, start by combining equal parts butter and flour in a pan to form a roux. Cook the roux until it reaches a smooth, paste-like consistency. Slowly add a splash of milk at a time, stirring constantly, and being careful not to over dilute the mixture. Continue until the sauce is silky smooth.

Once smooth, add the grated Gruyère cheese and stir until melted and fully incorporated. Season with salt, pepper, and a pinch of nutmeg, then add a spoonful of Dijon mustard. Stir to combine, and voilà—your béchamel sauce is ready.

To assemble the sandwich, slice your bread and toast it with butter in a pan until golden brown. Layer on the ham and Gruyère cheese, close the sandwich, and top with a fried egg for the "Madame" effect.

Serve with your partner, and enjoy your deliciously indulgent creation!