Cook the fettuccine in a large pot of salted boiling water according to package instructions until al dente.

While the pasta cooks, in a large skillet over medium heat, cook the guanciale or pancetta until crispy.

In a bowl, whisk together the eggs, grated Pecorino Romano, and a generous amount of black pepper.

When the pasta is done, reserve some pasta water and then drain the rest.

Add the hot pasta to the skillet with the guanciale, removing from heat.

Quickly pour the egg and cheese mixture over the pasta, tossing vigorously. Add reserved pasta water a little at a time until you reach a creamy consistency.