What is it?
Hollandaise sauce is an emulsion of egg yolks, liquid butter, and is seasoned with lemon juice. An emulsion is a type of mixture, where two or more liquids are mixed, but droplets of one liquid settles out from the other because they are immiscible.
Sauces Derived from this sauce
One sauce that derives from hollandaise sauce is Bearnaise. To make this sauce you add tarragon, white wine, vinegar, and shallots to your hollandaise sauce. Another sauce that is derived from this sauce is maltaise. To make this you add blood orange juice and zest to your hollandaise sauce.
What to do with it
Hollandaise sauce goes well over vegetables, such as asparagus, broccoli, or Brussels sprouts. The most common use for this sauce is to put it over eggs Benedict. This sauce could also be used over top of various sea foods, such as salmon.