Boil salted water for pasta.
Cut the guanciale into small pieces. Cook it in a skillet over medium heat for 2-3 minutes, stirring occasionally so it cooks evenly. Once the guanciale is ready, turn off the heat, and set it aside.
In a bowl, whisk together the eggs, Pecorino Romano, and black pepper till thick & creamy.
Cook the spaghetti most of the way, stopping before al dente. Do not drain.
Add spaghetti to the skillet with guanciale. Ladle in pasta water as needed to finish the pasta in with the guanciale. Pasta should develop glossy thickness.
Once pasta is fully cooked, add pasta to the bowl with the egg mixture in batches to not overcook the eggs. Stir in between additions. Pasta should be hot enough to cook the eggs creating velvety sauce. Serve immediately.
