Cook the spaghetti in a large pot of salted boiling water until al dente.

Meanwhile, in a skillet over medium heat, cook the diced guanciale until crispy. Set aside.

In a bowl, whisk together the egg yolks, grated Pecorino Romano, and Parmesan cheeses until well combined.

Drain the cooked spaghetti, reserving a cup of pasta water.

Immediately add the hot spaghetti to the skillet with the guanciale, tossing to coat.

Remove the skillet from heat and quickly stir in the egg and cheese mixture, using the reserved pasta water to loosen the sauce if needed.

Season generously with freshly ground black pepper and salt to taste.

Serve immediately, garnished with additional grated cheese and pepper if desired.