We first published this brief diversion on what makes a "genuine Philly cheesesteak" (Sept. 19, 2019) alongside our review of Rocky's on Country Club in Sherwood:
No matter what you've heard, seen or eaten, a real Philadelphia cheesesteak does not have green peppers. (Some places in the Philadelphia area do serve a sandwich, sometimes called a "Steak Royale," that adds green peppers and/or mushrooms to the basic cheesesteak. It costs more. And while it's based on a cheesesteak, it's not a cheesesteak.)
A real cheesesteak is never made with roast beef. At best it's sirloin, at worst it's chuck, but it is steak, shaved paper-thin and then chopped/shredded as it cooks on a flat, open grill (a few aficionados will claim it tastes best if you use yesterday's grease). Most places add the cheese on top while it's grilling so the cheese melts down into the meat.
What kind of cheese? It varies. Outside the Italian parts of town, most steak sandwiches are made by Greeks, who mostly use provolone or American. Under no circumstances whatsoever, however, will a true Philly cheesesteak come with Swiss or — ugh! — cheddar.
Jim's on South Street, one of the two Philadelphia establishments that lays claim to having invented the cheesesteak, asks customers if they want it "wit Wiz," meaning Cheez Whiz, or "widdout Wiz," which means they'll make it with white American. Mozzarella doesn't really have enough flavor to work, but by adding it and pizza sauce to the recipe and baking the sandwich in an oven until the roll crisps, you can create a pizza steak.
The onions, meanwhile, initially go separately onto the grill, then are added to the steak and cheese melange before it's scooped into a hoagie roll. Toasting the roll on the grill or popping the completed sandwich into the oven to toast is optional.