1. Bring a large pot of salted water to a boil. Heat a large skillet over medium heat. Add the oil, bacon and pancetta and cook, stirring until the fat has rendered and the bacon and pancetta begin to crisp.
2. Add the pasta to the boiling water and cook until al dente.
3. While Pasta is cooking: Add the onion and garlic to the skillet with the bacon and cook until the onion is softened, about 5 min. Pour off all but 3 Tbsp. fat and add 1 cup pasta water. Bring to a simmer and cook to reduce by half to create a sauce.
4. In a med bowl, whisk the egg yolks with ½ cup of cheese. Temper the egg yolks by slowly whisking in about ½ cup pasta water.
5. When the pasta is done (DO NOT DRIAN), remove from the water with tongs and add to the skillet that has the sauce and add the parsley. Toss to coat the pasta with the sauce. Remove skillet from the heat and gradually pour in the egg yolk mixture, tossing vigorously to cook the yolks and coat the pasta, without curdling the sauce. Add salt to taste; it may not need any as the bacon and the cheese are salty. Add the remaining ½ cup of cheese, toss again. IF the pasta mixture is too thick, ADD pasta water to thin sauce as desired. Serve immediately.
Adapted from Geoffrey Zakarian My Perfect Pantry