Where many other decadent pasta dishes get their richness from cream, carbonara gets it from a mix of egg, pasta water, and Pecorino. Because it’s a component in the sauce, the eggs are not cooked in the pan along with the other protein, guanciale, as being exposed to the high heat would cause them to scramble. Some recipes call for using only egg yolks, but this can cause some consistency issues. Yolks alone tend to create a very thick and sticky sauce, the opposite of what you want for carbonara, therefore, it’s better either to use whole eggs or a mixture of whole eggs and egg yolk for something a little richer. 

When you’re ready to start the sauce, mix the eggs together with the Pecorino and pepper and then set aside. Then, using some of the reserved starchy pasta water, the cooked pasta is transferred into the pan with the guanciale and stirred around so the pork fat coats the noodles. The pan is then removed from the heat, and the reserved pasta water is added in along with the egg mixture. As this is stirred, the heat from the pasta will gently cook the eggs, forming a very creamy and velvety sauce. 

It certainly makes for a rich and delicious dish, though it hardly resembles (in flavor or texture) the tomato-centered amatriciana.