A Bechemel sauce is made from a pale or white roux and milk.  Common sauces in this group include Creme', Mornay and Soubise.  To make a Bechemel sauce:

1.  Use a heavy gauge pot, make a white roux. 
2.  Combine a tablespoon of white roux to approximately 1 cup of milk.  Stir on low heat until thick. 
3.  For a thicker sauce, combine one tablespoon more of the roux to the milk.

Note:  This sauce is great for making Macaroni and Cheese or an Alfredo sauce for pasta.
This is considered the "King" of all sauce because of its diversity, simplicity and taste.
Patriot Fact

This classic white sauce was named after its inventor, Louis de Bechemel, a steward of King Louis XIV.