Bring a large pot of salted water to a boil. Add the spaghetti and cook according to package instructions until al dente.

Reserve 1 cup of pasta water, then drain the spaghetti.

In a skillet over medium heat, cook the diced pancetta until crispy, about 5-7 minutes.

In a mixing bowl, whisk together the eggs, grated Parmesan, Pecorino, and black pepper until well combined.

Add the hot spaghetti to the skillet with pancetta, tossing to combine.

Remove from heat and quickly pour in the egg mixture, tossing continuously to create a creamy sauce. Add reserved pasta water as needed to reach desired consistency.

Serve immediately, garnished with chopped parsley and additional cheese if desired.