Bring a large pot of salted water to a rolling boil. Add the spaghetti and cook according to package directions until al dente.

While the spaghetti cooks, heat a large skillet (large enough to hold the pasta later) over medium heat. Add the diced guanciale (or pancetta) and cook until crispy and golden, rendering its fat. Remove the crispy pork from the skillet with a slotted spoon and set aside, leaving the rendered fat in the pan.

In a medium bowl, whisk together the egg yolks, whole egg, and half of the grated Pecorino Romano cheese. Season generously with freshly ground black pepper. Do not add salt yet, as the Pecorino and guanciale are salty.

Before draining the spaghetti, reserve about 1/2 to 1 cup of the starchy pasta water. Drain the spaghetti and immediately transfer it to the skillet with the rendered pork fat. Toss to coat the pasta in the fat.

Remove the skillet from the heat. Immediately pour the egg and cheese mixture over the hot pasta, tossing vigorously and continuously with tongs. Gradually add a few tablespoons of the reserved hot pasta water, continuing to toss, until a creamy, emulsified sauce forms. The residual heat of the pasta will cook the eggs without scrambling them.

Stir in the crispy guanciale (or pancetta) and the remaining Pecorino Romano cheese. Taste and adjust seasoning with more black pepper if desired. Only add a tiny pinch of salt if absolutely necessary, as the cheese and pork are salty.

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