Get the pasta cooking. In a large pot, bring 4 quarts of water to a boil with 3 tablespoons kosher salt. Add 1 pound bucatini pasta to the boiling water and cook according to the package directions, until al dente.
Prep the egg and cheese mixture. In a medium mixing bowl, whisk 3 eggs, 1 cup freshly grated Parmesan cheese, 2 tablespoons chili crisp, and ½ teaspoon freshly ground black pepper until smooth, and set aside.
Cook the pancetta or bacon. Drizzle 2 tablespoons extra virgin olive in a cold, large skillet with 6 ounces diced pancetta or bacon and heat over medium-low. Cook until the fat has rendered and the pancetta is still tender but crisped to your liking, then transfer to a plate. Add 1 thinly sliced onion to the rendered fat in the skillet and cook until tender, 3-4 minutes. Remove from the heat and add the pancetta back to the skillet to warm.
Combine the pasta with the bacon and onion. Reserve 1 /2 cup pasta water, drain the cooked pasta, then add the pasta to the skillet with the pancetta and onion, tossing well to coat with the rendered fat.
Toss it all together! Slowly whisk ¼ cup hot pasta water into the egg mixture, stirring constantly so the eggs don't scramble. Off the heat, quickly add the egg mixture to the pasta in the skillet and toss well to make the sauce. If needed, add more pasta water while tossing the pasta to make the silky sauce. Add more salt and pepper to taste, dollop with more chili crisp if desired, and serve with more grated Parmesan cheese.
Notes
You can add 1-2 tablespoons of butter while tossing to make an extra glossy sauce.