Bring a large pot of salted water to a boil
Cook spaghetti or bucatini until al dente
Reserve some pasta water
Cook guanciale or pancetta in a pan until crisp
Whisk eggs with grated Pecorino Romano and black pepper
Drain the pasta and add it to the pan with the guanciale
Remove the pan from heat
Add the egg and cheese mixture
Toss quickly to coat the pasta
Add reserved pasta water a little at a time until creamy
Serve immediately with extra Pecorino Romano and black pepper