Bring 6 quarts of salted water to a boil. Add spaghetti and cook until al dente, 8-10 minutes. Reserve ½ cup of the pasta water, then drain.
Heat a 10.25-inch cast-iron skillet over medium heat for 4-5 minutes. Add the pancetta and cook until crispy, 3 minutes. Turn off the heat.
Whisk the eggs and cheese together in a small bowl.
Turn the skillet to medium and add ¼ cup of reserved pasta water and peas. Add spaghetti to the pan and toss.
Remove the skillet from the heat and add the egg mixture. Stir quickly until the eggs begin to thicken the sauce. Add more reserved pasta water as desired.
Season with cracked black pepper and salt. Serve immediately.
Keyword carbonara, cast iron skillet, pasta, spaghetti