Cut the guanciale into even pieces. Place it in a skillet and cook until it becomes crispy, turning from pink to golden brown and releasing its fat.

Prepare the egg. In a bowl, crack the egg, add black pepper, and mix. Add some of the Pecorino Romano and stir until you get a creamy mixture.

When the water boils, add the spaghetti. Cook for the time indicated on the package, but remove the pasta about 2 minutes early. Using a timer is helpful.

Keep the skillet warm. When the pasta is done, add it to the guanciale and toss well to coat and absorb the flavor for 1 minute. Turn off the heat, add the remaining Pecorino Romano, and pour in the egg mixture. Quickly toss everything together until the sauce is smooth and creamy. Plate the pasta, finish with another dash of freshly ground black pepper, and serve hot.