[cape chef]

I know we have had this discussion before, but I guess it deserves to be reincarnated once in a while.Grease, don't worry about what you do or don't know, just be open to learning.The topic of sauces in the French domain are quite specific and not really open to to much interpretation.

With that said.
It basically comes down to this.

Liquid + a thickening agent = a leading "mother" sauce
Leading sauce + additional flavorings = small sauces
As kuan said, a beurre blanc is an emulsion that is stabilized by the small amounts of lecithin naturally found in butter. This forms a temporary oil in water emulsion.

Although beurre blanc is similar in concept to hollandaise, it is not truly a leading sauce. Tomato sauce often is made with mire poix and smoked meats in regards to French mother sauce protocol.