Bring a large pot of salted water to a boil for the spaghetti. Heat 2 tablespoons olive oil in a large skillet over medium heat. Add the bacon/pancetta and onion and cook until the onion is caramelized and the bacon is crisp. By now, your water should be boiling. Add the spaghetti.

Meanwhile, in a large serving bowl, whisk together the eggs, half and half, and cheese. Scrape in the bacon and onion, along with the cooking fat.

Before draining the pasta, scoop out about 1/3 cup of the cooking water and whisk it into the bowl with the bacon and eggs. Drain the spaghetti and add to the bowl. Toss quickly and place a plate on top of the serving bowl to cover completely. Let sit for 5 minutes. Remove the plate and toss with black pepper and nutmeg (if using).