Bring an 8-quart pot of water to a boil. Add the pasta and 2 Tbs. salt and cook until al dente, about 1 minute less than the package directions, stirring often to prevent sticking. Reserve 1 cup of the water and then drain the pasta.
Meanwhile, put the guanciale or pancetta and olive oil in a 12-inch heavy-duty skillet (not cast iron), and cook over medium heat, stirring occasionally, until golden-brown but not yet crisp, 3 to 5 minutes for guanciale; 5 to 7 minutes for pancetta (you don’t want to render all the fat). Remove the skillet from the heat. In a medium bowl, whisk the eggs, Parmigiano, and 1/4 tsp. black pepper until well combined. Slowly whisk in 1/4 cup of the reserved pasta water.
Immediately after draining the pasta, add it to the skillet and then quickly pour in the egg mixture, tossing continuously with tongs, until the pasta is well coated, 15 to 30 seconds. Add more of the reserved pasta cooking water if needed to achieve a creamy consistency.
Serve hot, sprinkled with additional black pepper to taste.
nutrition information (per serving): Calories (kcal): 540; Fat (g): 23; Fat Calories (kcal): 200; Saturated Fat (g): 8; Protein (g): 26; Monounsaturated Fat (g): 10; Carbohydrates (g): 57; Polyunsaturated Fat (g): 2.5; Sodium (mg): 750; Cholesterol (mg): 135; Fiber (g): 2.