Bring a large pot of salted water to a boil. Add the spaghetti and cook according to package directions until al dente. Before draining, reserve about 1 cup of pasta water.

While the pasta cooks, heat a large skillet over medium heat. Add the diced guanciale and cook until crispy and most of the fat has rendered out, about 8-10 minutes. Remove the guanciale with a slotted spoon and set aside, leaving the rendered fat in the skillet.

In a medium bowl, whisk together the whole eggs, egg yolks, grated Pecorino Romano cheese, and black pepper until well combined and creamy.

Drain the cooked spaghetti and immediately add it to the skillet with the guanciale fat (off the heat). Toss to coat the pasta.

Quickly pour the egg mixture over the hot pasta, continuously tossing with tongs. Add a splash of the reserved pasta water, a tablespoon at a time, and continue to toss vigorously until the sauce emulsifies and becomes creamy, clinging to the pasta. Do not let the eggs scramble.

Stir in the crispy guanciale. Taste and adjust seasoning if needed (Pecorino and guanciale are salty, so usually no extra salt is needed).

Serve immediately, garnished with extra grated Pecorino Romano cheese and freshly ground black pepper.