This recipe is attributed to Fred Harvey, who began a chain of eateries along western railroad lines in the 1870s. They precede the advent of the luxury dining car. Harvey Houses became famous for their good food, and for their wholesome and chaste servers, who came to be known as "Harvey Girls."
~ from the book "Dining By Rail," by James D. Porterfield, 1993, St. Martin's Press, New York.
In the 2-quart saucepan, make a roux using the butter and flour; bring to a light brown color, about 2-3 minutes.
Meanwhile, combine milk and chicken stock in the smaller saucepan and heat just to boiling. Pour hot milk/stock mixture slowly into roux, stirring constantly with a whisk to prevent lumps. Cook over lowest heat for 30 minutes.
Strain sauce into the top of a preheated double boiler, place a dab of butter on top to prevent crust from forming, and set aside until needed.