1.
Place
butter in a saucepan and turn the heat to low. When the butter is melted,
remove the saucepan from the stove.
2.
Sift
the flour into the butter a little at a time, stirring continuously to
combine them.
3.
Whisk
in the milk a little at a time.
4.
Put
the saucepan back on the stove and slowly stir with a wooden spoon, until the
sauce starts boiling and becomes thicker.
5.
Turn
heat off. Add salt, and stir in the grated parmigiano cheese and pinch of
nutmeg.