Fill a large pot with water and season it generously with salt. Bring to a rolling boil.

Add spaghetti or bucatini to the boiling water. Cook until 'al dente', about 8-10 minutes. Reserve a cup of cooking water and drain pasta.

Heat a large skillet over medium heat. Add diced pancetta or bacon and smashed garlic. Sauté until bacon is crispy, about 5-7 minutes.

In a mixing bowl, whisk the whole eggs, egg yolks, Pecorino cheese, Parmesan cheese, and black pepper until smooth.

Add the hot, drained spaghetti to the skillet with crispy bacon. Turn off the heat and toss.

Quickly pour the egg and cheese mixture over the pasta and toss to coat, using residual heat to cook the eggs without scrambling them.

Gradually add reserved pasta water to achieve a creamy texture, tossing until sauce clings to pasta.

Taste and adjust seasoning with more cheese or pepper. Add fresh parsley if using.

Serve immediately with extra cheese and pepper on the side.