Many recipes call for egg yolks to be mixed with sugar. This mixture forms the basis of most custards, and desserts like sabayon/zabaglione. The technique is pretty simple, but one major thing that can go wrong is what some people call ‘burning the yolks‘. This happens when the yolks and the sugar remain in contact, without being whisked, for long enough that the sugar draws moisture out of the egg, which dried and hardens the yolk in spots.
This leaves what looks like grains of sugar that are darker than the rest of the yolk and cannot be melted or whisked out. While fairly dire if it does happen, there are pretty easy ways to avoid this.
The first is to pre-weigh out the sugar, so that you can add it all in one go, and avoid prolonged contact between sugar and egg while you weigh out the sugar into the yolks. The next is to whisk immediatly after adding the sugar, and not stopping until the mix is homogenous. This mixture can how sit for a while, but whisk it around every now and then and again right before you use it.
