Place the guanciale, cut into 0.25-inch batons, in a wide cold skillet. Cook over medium-low heat, stirring occasionally, until the fat renders and the pieces are golden and crisp, 10–12 minutes; transfer the crispy bits to a bowl, leaving the rendered fat in the skillet.
Salt the boiling water with the kosher salt, add the rigatoni, and cook until 2 minutes shy of al dente, 8–10 minutes; reserve 1.5 cups of the starchy cooking water.
Add about 0.5 cup hot pasta water to the rendered fat and add the black pepper. Simmer over medium heat, swirling, until emulsified and fragrant, 1–2 minutes.
Use a spider or slotted spoon to transfer the pasta directly to the skillet. Toss over medium heat, adding splashes of pasta water as needed, until coated and just al dente, 1–2 minutes.
Remove the skillet from the heat and add the Pecorino Romano in 2–3 additions, tossing vigorously and adjusting with more hot pasta water as needed to form a glossy, creamy sauce that clings to the pasta, 1–2 minutes.
Fold the crispy bits back into the pan and toss to combine. Let rest 1 minute to thicken slightly, then plate and serve immediately.