Melt butter in a saucepan. Add the flour and stir together until smoothly blended. Add milk gradually and whisk constantly until a blended and no lumps are formed. Season with nutmeg, salt, and pepper
FOR THE CROQUE MONSIEUR
Butter the slices of bread and fill with layers gruyere cheese and ham. On a skillet over medium heat add a dot of butter (or butter the bread) and place the croque monsieur over it and brown lightly both sides.
Warm the broiler. Place the croque monsieur on a cookie sheet, top with bechamel cream, and some more gruyere cheese. Broil until the cheese melts and gets a golden color.