When I was in high school, white sauce was the first lesson in home economics. In those long-ago days--the late 1930s--girls learned to cook and boys went to shop and learned mechanics. I remember stirring thick, bland, lumpy sauces which didn’t enhance otherwise decent leftovers.
But when white sauce is well made, it has a valuable place in many dishes and gives leftovers a pleasing reincarnation. It is ideally suited for this soup recipe.
When you want to make just a sauce and not a soup, and you are using it over rice, pasta or toast, reduce the amount of these ingredients by one-half or one-third. This freezes well.