In the culinary arts, the term "mother sauce" refers to any one of five basic sauces, which are
Béchamel, Velouté, Espagnol, Sauce tomate, Hollandaise.
Each of the five mother sauces is made with a different liquid, and a different thickening agent. White roux is cooked for just a couple of minutes, just enough time to remove the taste of flour. The longer it cooks the darker.
For the roux, in a saucepan melt butter and add flour – cook for 2 minutes stirring every so often. In order to avoid lumps, use cool roux and boiling liquid or hot roux and cool liquid. Lukewarm liquid works just fine on hot roux. Pour liquid all at once in the saucepan, bring to boil and cook for 2 minutes whisking constantly. Remove from the heat, add cream if desired and an egg yolk to color the sauce. Season sauce with salt, pepper and nutmeg to taste.
A mornay sauce is an enriched béchamel with cheese.