Heating the blender jug is the key step in homemade béarnaise sauce.
Béarnaise sauce is the classic accompaniment to a good steak, and a blender makes it easier if the jug is heated before use.
According to The New York Times, Béarnaise is a variation of Hollandaise, the creamy sauce used in Eggs Benedict. The main difference lies in the flavor: MasterClass notes that Béarnaise gets its acidity from a reduction of white wine vinegar flavored with shallots and tarragon.
That acidity helps to counteract the fat of the steak, so the sauce is an essential accompaniment to emulate the best steakhouses.
Making Béarnaise sauce by hand requires care. According to RecipeTin Eats, the egg yolks must be cooked very gently to achieve an emulsion between the vinegar, butter, and yolks; otherwise, you'll end up with scrambled eggs or a runny sauce. MasterClass recommends adding the other ingredients gradually, whisking constantly, and the New York Times uses a double boiler to whisk the yolks without letting them curdle.
Using a blender simplifies the process. Justin Chapple of Food & Wine adds the vinegar reduction and butter gradually to the egg yolks, and the machine does almost all the work. The key step is to heat the blender jar, because, according to Food & Wine, this prevents the butter from hardening when added.
To heat it, simply fill the jug with warm water just before using it, empty it, and dry the inside with a towel to remove any remaining moisture.
