Heat a large pot of well-salted water to a boil, then add spaghetti and cook al dente, according to instructions.
Meanwhile, in a medium bowl, whisk eggs, yolk and cheeses, and season with a bit of salt and a lot of fresh black pepper. Set aside.
Heat a small frying pan to medium and add a teensy bit of olive oil (depending on pan and meat you may want to prevent sticking). Then add guanciale and shallots, and cook, stirring occasionally until browned a bit and cooked through. Turn off heat and set aside.
When pasta is done, reserve 1 cup of cooking liquid, then drain the pasta. Put the pasta back into the large pot and add the guanciale/shallots and stir to combine. If needed, heat the mixture on medium until warmed through then turn off the heat, and stir in the egg mixture, combining quickly, and adding a bit of pasta water as you go to get it creamy.
Serve immediately with additional grated pecorino and black pepper. Buon appetito!
Buon Appetito!!
Notes
Use Dried Pasta - I've been told this works better with dry spaghetti to help the sauce stick, and it's also more authentic to its roots as a "peasant dish" as well.