Cut Guanciale (or bacon) into 1/2 inch (1 cm) pieces.
Put your Guanciale in a saucepan, and start browning it on low heat.
Boiling water in a large pot. When it's boiling, add salt and spaghetti. Cook it al dente (Usually 7-8 minutes). Pay attention to how much salt you use, Guanciale or bacon might be very salty.
In the meantime, make the "sauce" for your authentic spaghetti carbonara. Put 4 yolks and one whole egg in a large bowl.
Add grated Pecorino cheese (or Parmigiano Reggiano), and salt and pepper to taste (again, be careful with the salt).
Mix the egg and Pecorino with a whisk.
When the guanciale is crisp and brown, put it in a plate and let it cool.
Once the guanciale reached room temperature, add it to the egg-Pecorino mix and stir. You don't want to make this while the Guanciale is still hot, as you're not making scrambled eggs.
Once the pasta is cooked al dente, you have to work fast. The sauce of authentic spaghetti carbonara is basically eggs and Pecorino cheese forming a rich, creamy sauce by the heat of the spaghetti. Be it too cold, you won't get a real sauce. Be it too hot, you get spaghetti with scrambled eggs. Drain the spaghetti, wait for a few seconds, and toss it in the egg-Pecorino mix.
Your authentic spaghetti carbonara is ready. Serve hot.