Thickening with egg yolks provides a nuanced rich flavor. Sauces like hollandaise are classically thickened this way. Egg yolk can be more difficult to work with than some other thickening agents because overheating will cause the egg yolk to curdle.Beat the yolks until they appear consistently smooth and slightly frothy.


Use 2 to 3 egg yolks per cup of liquid sauce you want to thicken.
The more egg yolks you use, the thicker the resulting sauce will be.
 First, bring the beaten egg yolks to room temperature to prepare them for tempering. Don’t try to speed up this process by using heat. Take some of your hot sauce that you want to thicken, and add it gradually to the beaten egg yolks. This will slowly raise the temperature of the yolks and prevent them from curdling.
 To thicken with egg yolks, it is best to use a thermometer while you are tempering the yolks. You want to add enough sauce to the yolks to bring them to the same temperature as your sauce. For the best thickening, this temperature should stay between 149 (65 degrees Celsius) and 158 degrees Fahrenheit (70 degrees Celsius).
 Stir until the two are blended. After you add your egg yolks, avoid letting the sauce get above 190 degrees Fahrenheit (32 degrees Celsius). If the temperature of your sauce is too high, your egg yolks could curdle.
Use a whisk or fork to rapidly beat your egg yolks.
Temper the yolks.
Use a thermometer.
Stir the tempered egg yolk mixture into the sauce.
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