01 - Bring a large pot of salted water to a boil. Cook the pasta according to package instructions until al dente. Reserve 1/2 cup pasta cooking water, then drain.
02 - While pasta cooks, heat olive oil in a large skillet over medium heat. Add beef bacon strips and cook until crisp and golden, about 5–7 minutes. Remove from heat.
03 - In a bowl, whisk together eggs, grated Parmesan, Pecorino (if using), black pepper, and salt until well combined.
04 - Add drained pasta to the skillet with the beef bacon (heat off). Quickly pour in the egg-cheese mixture, tossing vigorously to coat the pasta. Add reserved pasta water, a little at a time, until the sauce is creamy and silky.
05 - Divide immediately between two warmed plates. Sprinkle with extra Parmesan, more black pepper, and parsley if desired.