What technique is used to thicken Hollandaise sauce?

The technique used to thicken Hollandaise sauce is whisking over a Bain Marie. A Bain Marie, or water bath, is a gentle method of applying heat to ensure that the sauce is warmed slowly and evenly. This is crucial for emulsifying the egg yolks and the clarified butter without cooking the eggs too quickly, which can lead to curdling.

When the egg yolks are whisked over the Bain Marie, the heat allows them to thicken and emulsify with the butter, creating a smooth and creamy texture essential to Hollandaise. This careful temperature control is critical because it prevents the sauce from becoming too hot and seizing, resulting in a perfect emulsification.

In contrast, techniques such as blending, boiling, and steaming do not provide the controlled heating that is necessary for proper emulsification in Hollandaise sauce, making whisking over a Bain Marie the ideal method.