Fry the cubed guanciale in a pan until it's crispy on the outside but still soft in the middle.
Separate the 'bacon' and the fat in the pan and let the fat cool down until hand warm.
Mix the egg yolks, parmesan, and the fat in a bowl and let it sit for a while (you will see how the textures changes a bit).
Mix the spaghetti, the sauce, pepper and guanciale. You 'cook' the egg mixture with the remaining heat of the pasta while mixing in the 'sauce'. Not too cold, not too hot. (only let cool briefly). That's one of the difficulties.
Now add the noodle water while mixing until you get the creaminess you want.