Eggs - Prevent Burning for Egg Yolks

QUESTION: Egg yolks seem to “cook” when we mix the sugar and yolks to make pastry cream. How do we prevent this?
SARAH SAYS: When combining egg yolks and sugar, make sure that you mix together immediately, otherwise the yolks will quickly dry out from the undissolved sugar, called "burning". This will leave you with hard bits in the finished recipe i.e., crème anglaise, pastry cream, lemon curd, etc.

This how to baking technique is used with the:
Chocolate Thick Pastry Cream Recipe Tutorial

1. Whisk the yolks, and add the sugar to them in a bowl.

2. Immediately mix the ingredients together with a whisk for about 30 seconds.

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