1/2 cup butter
1/2 cup all-purpose flour
4 1/2 cups whole milk
Pinch freshly grated nutmeg
Kosher salt and freshly ground black pepper
If the sauce is too thick, add a little more milk, if too runny, return to the heat and add a pat of butter mixed with an equal amount of all-purpose flour. The most important thing though is: besciamella should not taste floury. If you think your sauce is ready, but you can spot a hint of "flouriness" when you taste it, think again, and keep on cooking it for a few minutes more.