Hollandaise Sauce is an egg based sauce flavored with a bit of lemon or vinegar, butter and a hint of cayenne pepper. Hollandaise sauce is typically prepared in a double boiler to ensure the sauce does not scorch or burn.
The sauce is served over vegetables, fish, or Eggs Benedict. In France, traditionally this sauce would sit alongside the food it is being served with and never ladled over it.
You can view a recipe for making your own hollandaise sauce here.
You can purchase ready made version of this sauce at your local grocery store. Brands such as Knorr are readily available. These are in powder form and you typically add butter and milk. There are also some brands such as Maille that are ready to heat and serve. These can all be purchased online at Amazon.com: Hollandaise Sauce