Before you start, steady yourself
Creating a base to hold the bowl with the egg mixture will free up your hands while you drizzle in the hot liquid and simultaneously whisk the eggs. I use a twisted-up dish towel and one of those sticky mats for opening up tight jars.
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
Heat the cream or milk until it's hot and steamy, but not quite boiling.
Gradually, whisk in some of the hot liquid
Drizzle in a portion of the hot liquid into your egg mixture while whisking constantly. Pour in enough hot liquid to make the egg mixture hot. This process heats up the eggs relatively quickly and gently, and dissolves any sugar in the mixture. It won’t get hot enough to coagulate; instead, this process gets you closer to the temperature at which the mixture will thicken.
Add the tempered liquid to the hot pot
Pour the heated, tempered eggs into the remaining hot liquid while stirring over a low to medium heat.
Continue stirring over low heat with a wooden spoon or heat-proof spatula and cook until the mixture begins to thicken, according to your recipe.
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
The classic dessert sauce is also the basis of many ice cream recipes. Tempering is essential to this preparation.
Case Study 2: Spaghetti Carbonara
A lot of people swear by a tempered carbonara sauce. I’ve done it fine both with and without tempering. One of the most important things to do is toss the egg mixture with the pasta off the heat, just after it's drained. The pasta should be hot enough to thicken the egg mixture without having to return it to the stove.
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.
Case Study 3: Cornstarch-thickened pudding
A pudding, custard, or pastry cream is often made with tempered eggs, but you can get around it. Mix the egg, milk/cream, and starch together before heating them. The downside is that you have to keep a watchful eye over it the whole time and keep stirring to make sure the eggs don’t get lumpy.