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

While the pasta cooks, heat a large skillet over medium-low heat. Add the diced guanciale and cook slowly until crispy and the fat has rendered. Remove the guanciale 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, finely grated Pecorino Romano cheese, and black pepper until well combined and creamy. Do not add salt to this mixture yet, as the guanciale and Pecorino are salty.

Before draining the pasta, reserve about 1 to 1.5 cups of the starchy pasta water. Drain the spaghetti and immediately add it to the skillet with the rendered guanciale fat. Toss to coat.

Remove the skillet from the heat. Quickly add the egg and cheese mixture to the hot spaghetti, tossing vigorously and adding a splash of the reserved pasta water as needed (1/4 to 1/2 cup usually) to create a creamy, emulsified sauce. The heat from the pasta will cook the eggs just enough to create the sauce without scrambling them.

Stir in most of the crispy guanciale, reserving some for garnish. Taste and adjust seasoning if necessary, adding a tiny pinch of salt only if needed (usually not required due to salty cheese and guanciale).

Serve immediately, garnished with the remaining crispy guanciale, extra Pecorino Romano, and a final grind of black pepper.