The main difference between Amatriciana and Carbonara
While many other fine pasta dishes get their richness from cream, carbonara gets it from a combination of eggs, pasta water and pecorino. Because it is an ingredient in the sauce, the eggs are not cooked in the pan with the other protein, guanciale, because exposure to high heat would cause them to scramble. Some recipes call for using only egg yolks, but this can cause some consistency issues. The yolk alone tends to make for a very thick and sticky sauce, which is the opposite of what you want for carbonara, so it’s best to use whole eggs or a mixture of whole eggs and egg yolks for something richer.
When you’re ready to start the sauce, mix the eggs with the pecorino and pepper and set aside. Next, using some of the reserved starchy pasta water, transfer the cooked pasta to the pan with the guanciale and stir until the pork fat covers the pasta. Then remove the pan from the heat and add the reserved pasta water with the egg mixture. When this is stirred, the heat of the pasta will gently cook the eggs, forming a very creamy and velvety sauce.
It certainly makes for a rich and flavorful dish, although it’s nothing like (in flavor or texture) the tomato-centric Amatriciana.