Prepare your crème fraîche (use heavy cream as substitute). Take it out of the refrigerator before you start cooking. You want it to be at room temperature by the time it's needed.
Cut the bacon into little 1/2-inch pieces.
While you're chopping up the bacon, cook the pasta. Heat 4 quarts of water and the salt to a rolling boil.
Gradually stir in pasta; return to boiling. Boil, uncovered according to recommended time on pasta package, stirring occasionally.
After the bacon has been chopped, it's time to dice the onion. Peel the onion and dice it to 1/2-inch (or whichever size you prefer).
Prepare the egg yolk by draining the egg white from the egg. You can save the whites for future use (I save mine in the freezer).
Sauté the bacon in a flat pan over medium-high heat until slightly browned.
Add the onions to the pan along with a pinch of salt, stir well. Cook until the onion sweats (softened and translucent).
Add the crème fraîche to the pan. Stir thoroughly with the rest of the ingredients. Turn off the heat about after 30 seconds.
Quickly stir in the egg yolk, and grind in some fresh black pepper.
Drain the pasta.
Return the pasta back to the pot.
Quickly mix in the sauce while the pasta is still hot.
Grate the cheese into the pot.
Add more cheese if desired.
A delicious and filling meal is served. Enjoy!