Cut pancetta (or bacon) into pieces about 1" wide.  Cook until browned and crisp and set aside, saving bacon grease in the skillet.

Cook linguine in salted water until al dente.

Add chopped onions to bacon grease and let them cook down over a medium-high heat for a couple of minutes.  Throw in the garlic.  Allow to cook for another couple of minutes, then remove with a slotted spoon.  Discard any remaining grease.

Place the pan back on high heat until it starts to smoke a little.  As soon as the pan begins to smoke, pour in half the chicken stock (or the white wine, if using).  Whisk until pan is thoroughly deglazed and all of the brown bits have come off the bottom of the pan.  Add the rest of the chicken stock.  Return onion and garlic to the pan.  Let simmer over medium heat.

Crack the eggs into a large bowl.  Add most of the Parmesan cheese, and roughly chop the parsley, adding most of it in as well.  Leave a little Parmesan and parsley out for a garnish.  Mix well with a whisk or fork.

Add the cooked hot pasta to the egg mixture and then add the onion mixture.  Stir in the butter and cooked bacon.  Mix it all together well.  Add pepper to taste.  Garnish with parmesan and parsley.  Throw out all previous carbonara recipes.