There are so many versions of this .......mine tastes different every time . . . . I try to keep to the authentic Italian version that has absolutely no cream and huge chunks of pancetta. The flavor of the dish will always depend on the saltiness of the bacon and different additions.
You can also add a splash or white wine after the bacon is almost finished. —blanka.n
First whisk up your eggs and egg yolks in a large bowl that you will drop the pasta in.
Add Parmesan - about a half a cup, freshly ground pepper. Set aside.
Fry pancetta in a pan til crisp. Remove with a slotted spoon and quickly add onion and garlic, either or both into bacon fat and cook til done or add a bit of EVOO or add a splash of white wine til it's evaporated.
Boil pasta (Spaghetti or Fetucini) according to package directions.
When pasta is cooked combine with the egg/cheese mixture and bacon and onion.
Season to taste. Make sure everything is well incorporated and add some pasta water if necessary.