Put 3 liters of well-salted water in a pot and let it boil. When it starts boiling add the pasta and cook for 8-10 minutes, until they become al dente.
While the pasta is boiling, heat a large pan on medium heat. With very little olive oil (half a tablespoon), sauté pancetta or bacon for about 3 minutes, or until crisp. Then turn off the heat.
In a small bowl, mix the eggs and the cheeses until they are well mixed.
When the pasta is ready, take 1/2 cup of the pasta water and drain the rest.
Turn on the heat, in moderate temperature, and put the pan with the bacon on. Add the water from the spaghetti. Put the spaghetti in the pan and mix by shaking the pan over the fire for a few seconds until the most of the water evaporates.
Remove the pan from the heat and add the egg mixture and mix quickly until the eggs are tightened. The eggs will be cooked by the remaining heat. If the sauce looks too thick, add some more of the pasta water.
Sprinkle with freshly ground black pepper and serve immediately!