Bearnaise Sauce
Béarnaise sauce is a sauce made of clarified butter, egg yolk, white wine vinegar, and herbs. It is regarded as a "child" of hollandaise sauce. The difference is only in the flavoring: béarnaise uses shallot, black pepper, and tarragon, while hollandaise uses white pepper or a pinch of cayenne. The sauce's name derives from the province of Béarn, France. It is a traditional sauce for steak. Legend has it that the sauce was accidentally[dubious – discuss] invented by the chef Jean-Louis-François Collinet, the accidental inventor of puffed potatoes (pommes de terre soufflées), and served at the 1836 opening of Le Pavillon Henri IV, a restaurant at Saint-Germain-en-Laye. The restaurant was in the former residence of Henry IV of France, a gourmet himself, who was from Béarn.
Source: Wikipedia