Prepare the Egg + Cheese Mixture: In a bowl, whisk together the eggs, grated Pecorino Romano, and Parmesan cheese. (add a bit of pepper if desired). Set aside. This will be your creamy sauce.
Boil the Pasta: Fill a large pot with water, add a tablespoon of salt, and bring it to a boil. Cook the spaghetti according to the package instructions until it's al dente (cooked but still a bit firm).
Cook the Pancetta (or Bacon): While the pasta is cooking, add the diced pancetta (or bacon) to a skillet over low heat. Cook slowly over low heat until it becomes crispy and golden brown and the fat is rendered. If you like, you can add minced garlic for extra flavor.
Combine Everything: Once the pasta is cooked, reserve about a cup of pasta cooking water and drain the rest. Add the hot, drained pasta to the pan with the pancetta. Toss everything together so the pasta gets coated with the delicious flavor of the pancetta.
Add the Creamy Sauce: Remove the pan from heat. Add 2 tablespoons of the reserved pasta water. Pour the cheese and egg mixture over the pasta. Toss everything quickly and thoroughly. The heat from the pasta will cook the eggs and create a creamy sauce.
Adjust Consistency: If the sauce seems a bit too thick, add a little bit of the reserved pasta cooking water gradually until you reach the desired consistency.
Season and Garnish: Season the carbonara with black pepper and salt to taste. Garnish with fresh parsley and more shredded parmesan cheese if you like.
Serve Immediately: Carbonara is best served immediately. Enjoy your creamy and flavorful pasta!