Before you start, steady yourself
In the nest you made, place your bowl of whisked-up eggs and any sugar, cornstarch, spices, or salt that your recipe calls for.
Heat up the liquid
Gradually, whisk in some of the hot liquid
Add the tempered liquid to the hot pot
Generally speaking, to avoid curdling, you should not go higher than 180°F. If you are making a low-fat custard, the eggs will curdle at a lower temperature. If the mixture has cornstarch or flour in it (like an egg-based pudding), you’ll need to bring it to a boil for a short while for it to thicken. (Don’t worry, the starch will reduce the risk curdling.)
Even if you tempered the eggs well, you’ll likely have a few lumpy bits. So strain it before moving on. But do not strain if there's cornstarch in the mix—straining it will break up the starch structure that is helping the custard set.
Case Study 1: Crème Anglaise
Case Study 2: Spaghetti Carbonara
Tempered Method: Drizzle a ladleful of hot pasta water or hot cream into egg and cheese mixture, while whisking and then toss with hot (and cooked) pasta and guanciale, pancetta or bacon.
Non-Tempered Method: Toss egg and cheese mixture with the hot pasta and the crispy cured pork of your choice.