Bechamel Sauce also known as white sauce, it is made with a roux of butter and flour cooked in milk. It is one of the mother sauces of French cuisine and is used in many recipes of Italian cuisine, for example lasagne. It is used as the base for other sauces (such as the Crème sauce or Mornay sauce, which is Béchamel with cheese).
I've been on the search for a SW friendly way to make a white sauce. I tried a cottage cheese version with not much success. I then came across a yoghurt version so thought I'd give it a whirl. It totally gets the thumbs up from me. Best syn free 'white sauce' I've come across for sure.