Cook the spaghetti in abundantly salted water until al dente.

While you are cooking your spaghetti, whisk egg with grated pecorino cheese and lots of freshly ground pepper. (For most palates, if you salt the pasta water sufficiently and given that pecorino and pancetta are already quite salty, you need not season the sauce with salt.)

Separately, in a skillet, sauté the cubed pancetta in olive oil (or, if you really want to be authentic, lard) over moderate heat until the pancetta fat is translucent and just beginning to brown a bit. You do not want the pancetta to become crispy.

Once the spaghetti are cooked al dente, drain them (but not too well) and pour them into the skillet over very low heat. Make sure there is a bit of pasta water clinging to the pasta; if not, add a ladleful from the pasta pot. Mix well and then add your egg mixture and mix again. Keep mixing until the eggs just being to thicken and form a creamy sauce that clings to the pasta. If you prefer (and these days I tend to like my carbonara this way) or if you are worried about contamination, you can continue a bit longer until the eggs actually set. In either case, remove from the heat as soon as it just bit less done than you want, as the eggs will continue to cook from the residual heat of the pasta.

Serve immediately in warm pasta plates with additional pecorino and ground pepper if you like.