Bring a large pot of salted water to a boil. Add the spaghetti and cook according to package directions until al dente.
While the pasta is cooking, dice the guanciale (or pancetta) into small pieces.
In a large pan, cook the guanciale over medium heat until crispy. Remove the guanciale from the pan and set aside, reserving the rendered fat in the pan.
In a bowl, whisk together the eggs, egg yolk, Pecorino Romano cheese, and black pepper until well combined.
Drain the spaghetti, reserving about 1 cup of pasta water. Add the spaghetti to the pan with the reserved guanciale fat. Toss to coat.
Remove the pan from the heat. Gradually pour the egg mixture over the spaghetti, tossing constantly to prevent the eggs from scrambling. Add a little pasta water at a time if needed to create a creamy sauce.
Add the crispy guanciale to the pasta and toss to combine. Serve immediately, garnished with extra Pecorino Romano cheese and black pepper.
