Start by boiling a large pot of salted water. Once boiling, add the spaghetti and cook according to package instructions until al dente.
While the pasta is cooking, cut the pancetta into small cubes. In a skillet over medium heat, cook the pancetta until it becomes crispy, about 5-7 minutes. Then remove from heat and set aside.
In a mixing bowl, whisk together the eggs, grated Parmesan, grated Pecorino, and a generous amount of freshly ground black pepper until well combined. Set the mixture aside.
Once the spaghetti is cooked, reserve about 1 cup of the pasta cooking water, then drain the spaghetti in a colander.
Quickly add the hot spaghetti to the skillet with the pancetta, tossing to combine.
Remove the skillet from heat and allow the pasta to cool slightly (about 1 minute).
Gradually pour the egg and cheese mixture over the pasta, tossing continuously to create a creamy sauce. If necessary, add a little reserved pasta water to achieve the desired consistency.
Serve immediately, garnished with additional grated cheese and freshly ground black pepper if desired.