Cut the guanciale into 1/4 inch strips, and then cut each strip into 1/4 inch batons. (Tip: freezing the guanciale for 15-20 minutes can make it easier to slice).
Place a large skillet over a medium-low heat, and add the olive oil. When the oil is heated, cook the guanciale, stirring often, for about 10 minutes or until golden and crispy. It will shrink as it cooks!
Use a slotted spoon to transfer the cooked guanciale to a small plate, leaving the rendered fat in the skillet, remove from heat.
Meanwhile, cook the pasta in a large pot of boiling water (generously salted). When the rigatoni is halfway cooked, remove and drain the pasta (reserving 1.5 cups of the pasta water).
Add 3/4 cup of the pasta water to the skillet with the guanciale fat and place back on the heat to bring to the boil. Cook for 1 minute, swirling often to encourage it to emulsify.
Add the rigatoni to the skillet and cook until al dente. You can add more pasta water if necessary to keep the rigatoni coated in the emulsified sauce (it should be thick and glossy).
Increase the heat to medium-high, and add the cooked guanciale, black pepper, and 2/3 of the pecorino romano. Toss well to combine as the cheese melts.
Serve immediately, topped with the remaining cheese.