Sauce Béarnaise was developed in France around 1830.
It has became popular again because it goes well with grilled meat and fish, which are popular now.
There are three main steps in making the sauce:
- Boiling wine, vinegar, chopped tarragon and shallots in water, until the amount of liquid is reduced;
- Add egg yolks and slowly heat until it begins to thicken;
- Beat in melted butter until desired texture is reached, then strain.
If it is overheated, the egg yolk protein will coagulate (e.g. curdle), and you are beat. You can help prevent this by using enough wine and vinegar to keep the mixture acidic — so don’t try to substitute water.
The butter gets incorporated in the mixture because of the emulsifiers in the egg yolk. The fresher the eggs, the better these emulsifiers. In a pinch, as a last-ditch attempt to salvage a sauce, you can use a teeny bit of lecithin if you have it on hand. Lecithin is an emulsifier contained in egg-yolks, but the stuff we buy is now made from soy. Still, it may give the emulsification process enough of a helping hand to save the day.