Bring a large pot of salted water to a boil. Add spaghetti and cook until al dente, about 8 minutes.

While the pasta cooks, heat a large skillet over medium heat. Add the guanciale and cook until it is crispy and the fat has rendered, about 5-7 minutes.

In a mixing bowl, whisk together the eggs, Pecorino Romano cheese, and black pepper.

Drain the pasta, reserving 1 cup of the pasta cooking water. Add the hot pasta to the skillet with guanciale. Mix well to coat the pasta in the fat.

Remove the skillet from heat. Quickly pour the egg and cheese mixture over the pasta, tossing continuously to coat the pasta and prevent the eggs from scrambling. If the sauce is too thick, add reserved pasta water a little at a time until desired consistency is reached.

Season with salt to taste and serve immediately with additional cheese if desired.