Guanciale is cured pork jowl and is a familiar ingredient in Italian kitchens. Chef Michael Symon explains, "Like pancetta, it's not smoked, so it has a cleaner taste than bacon. And because it's not mass-produced, you're typically getting a heritage breed hog, so the flavor is more robust and porky." If you want to try it, Michael loves Iowa's La Quercia brand (laquercia.us).
Stirring a yolk into the hot pasta is molto autentico, but if it makes you squeamish or you're concerned about food safety, just whisk 4 whole eggs together in Step 3, then continue as instructed. (One benefit of this method is that you can help yourself to a more modest portion of pasta.)