Cook the Pasta: Bring a large pot of salted water to a boil. Add the pasta and cook until al dente, about 8–10 minutes. Reserve 1 cup of pasta water and then drain the pasta.
Cook the Pancetta or Guanciale: While the pasta is cooking, heat a large skillet over medium heat. Add the diced pancetta or guanciale and cook until crispy, about 3–5 minutes. Set aside, leaving the rendered fat in the pan.
Make the Egg Mixture: In a large bowl, whisk together the eggs, freshly grated Pecorino Romano, Parmigiano-Reggiano, and black pepper.
Combine Pasta and Egg Mixture: Add the hot, drained pasta to the skillet with the pancetta or guanciale, tossing it in the fat to coat. Remove from heat and quickly pour the egg and cheese mixture over the pasta, tossing to combine. The residual heat will cook the eggs, forming a creamy sauce. If the sauce is too thick, add reserved pasta water a tablespoon at a time to adjust the consistency.
Serve: Divide the Pasta Carbonara into bowls and garnish with extra cheese and black pepper. Serve immediately.