Put the guanciale in a saucepan and start browning it over low heat.
Bring a large pot of water to a boil. When it comes to a boil, add salt and the spaghetti. Cook it al dente (usually 7–8 minutes). Be careful with the salt, since guanciale or bacon can already be quite salty.
In the meantime, make the “sauce” for the authentic spaghetti carbonara. Put 4 egg yolks and 1 whole egg in a large bowl.
Add the grated Pecorino cheese, and salt and pepper to taste (again, be careful with the salt).
Whisk together the eggs and Pecorino.
When the guanciale is crisp and browned, transfer it to a plate and let it cool.
Once the guanciale has cooled to room temperature, add it to the egg-and-Pecorino mixture and stir. You don’t want to do this while the guanciale is still hot, unless you want scrambled eggs.
Once the pasta is cooked al dente, you have to work fast. The sauce in authentic spaghetti carbonara is basically eggs and Pecorino cheese turned into a rich, creamy sauce by the heat of the spaghetti. If it’s too cold, you won’t get a proper sauce. If it’s too hot, you’ll end up with spaghetti and scrambled eggs. Drain the spaghetti, wait a few seconds, and toss it with the egg-and-Pecorino mixture.
Your authentic spaghetti carbonara is ready. Serve immediately.