“So…it’s like a cracker with Cheese Whiz on it?”

This is how a friend from Seattle interpreted my explanation of the St. Louis-style pizza from my childhood. To be fair, St. Louis pizza is an acquired taste, and outsiders who try it for the first time tend to experience an emotion that lies somewhere between anger and bewilderment. Even in an article in which he lovingly defended St. Louis' much maligned dish, food guru Kenji López-Alt wrote that it wasn’t pizza at all, but a “big pizza-flavored nacho.” So why do people from St. Louis love it so much?

Well, it starts with the cheese. Provel cheese is the single most important ingredient; it’s what makes St. Louis pizza St. Louis pizza. Judah Friedlander of 30 Rock fame, who claims to be obsessed with Provel, described it in an NPR story as “melted plastic from the 80s…It’s disgusting and delicious.”

Provel cheese is not actually cheese at all. It’s a cheese product, moderately similar to Velveeta or, yes, Cheese Whiz, though it more closely resembles actual cheese than either of those two. Provel is an amalgamation of provolone, Swiss and cheddar cheeses, along with some liquid smoke. But most importantly, being a "cheese product" means that Provel also has extra fat and moisture added to it, as well as chemical salts that help it to melt. This last part is key, because the most lovable aspect of a St. Louis pizza is undoubtedly its excessively melty, gooey cheese top.

If you’ve never been to St. Louis, chances are you’ve never heard of – let alone tasted – Provel, which is almost exclusively available in the St. Louis (it exists in locations across the country, but it's extremely rare). So I’ll tell you that the cheese mysteriously starts out just as gooey when it goes into the oven as it does when it comes out, which makes for great leftover pizza.

St. Louis pizza’s crust is also its own quagmire: an ultra-thin disc of unleavened dough that isn’t much bigger than a frisbee, cut into squares so that perimeter pieces are oddly shaped and center pieces have no crust;both of these qualities are also identifiers of true St. Louis-style pizza.

Why do St. Louis pizzerias leave yeast – the very thing that makes bread rise – out of their dough? That’s a bit of a mystery as well, but the result is a crust that resembles a cracker (or perhaps more accurately, matzo) as much as it does pizza crust.

But St. Louis pizza certainly has no shortage of fans in the city it calls its own. PBS darling Lidia Bastianich has a recipe for St. Louis-style pizza in her cookbook, Lidia’s Italy in America. On an episode of Jimmy Kimmel Live, the host had a pie shipped in from Imo’s in St. Louis for guest Jon Hamm, a St. Louis native. And while Kimmel used the opportunity to discuss what he deemed “terrible pizza,” Hamm defended his hometown pie.

But Kimmel represents a vast majority of the population who find the dish either terrible or confusing. For those who love it though, St. Louis pizza is the only pizza. (I’m still on the fence).

So who decided to stick some gloppy processed cheese no one in the rest of the country has ever heard of on top of a glorified cracker and pop it in the oven?

Well, if you ask your average St. Louis native, the answer would be probably be the founder of Imo’s, the restaurant that claims to make the “original St. Louis style pizza.” But according to Jeff Parrott, operating partner at Farotto’s Pasta & Pizzeria, the answer is more complicated than that.

Parrott says his family helped St. Louis-style pizza get its start in 1956, when their restaurant oozed onto the scene.

“Everyone credits Imo’s for starting St. Louis-style pizza,” Parrott says. “But my uncle and father were using Provel since we opened. We’ve had the same recipe for our crust since day one. My uncle’s parents were from northern Italy, and that’s where the recipes for our sauce and crust came from.”

Still, Parrott doesn’t claim Farotto’s was the original. He says Luigi’s, which opened in 1953, came first in the city, but Farotto’s is the oldest St. Louis-style pizzeria currently running with the same family ownership.

Regardless of who invented the polarizing pizza style, Imo’s Pizza – which opened six years after Farotto’s in 1964 – undeniably popularized it. The chain now has more than 100 locations across St. Louis and a few in Illinois. And if that’s not enough proof of the chain’s dominance, Imo’s actually owns the rights to Provel.

Provel was trademarked in 1947 by J.S. Hoffman company in Chicago, and permission was granted in 1950. The trademark is now held by Churny, which is a subsidiary of Kraft, but the rights are all Imo’s.

“In 1964 when Ed and Margie (Imo) started Imo’s, they used Provel on their pizzas,” says says Nick Palank, Sales Manager for Imo’s. “They really liked it, so they bought the rights to it...If you’re a restaurant in Seattle and want to put Provel on your menu, you have to come to Imo’s to buy it.”

There are just a handful of spots across the country that serve pizza that even resembles St. Louis-style pizza. San Francisco’s Tony’s Pizza Napoletana; Denver’s City Pizza and Pasta; Allen, Texas’ 5th Street Pizza; and Palm Harbor, Florida’s Jake’s Pizza all make their own versions of St. Louis pizza.

But a St. Louis-inspired pie can most famously be found at New York's Speedy Romeo, co-owned by St. Louis native and former Chopped contestant Justin Bazdarich. And how do notoriously stubborn, pizza-obsessed New Yorkers feel about the Provel-topped pie?

The “St. Louie” – which also has San Marzano tomatoes, pickled chilies, pepperoni and Italian sausage – is the much-loved pizza joint’s top seller. Speedy Romeo also has a white pie ("The White Album") with Provel, but it should be noted that both offerings are served on Neapolitan crust that in no way resembles a cracker, perhaps providing evidence that it's not Provel's fault St. Louis pizza has a bad rap.

For so many in my proud city, this strange under-the-radar pizza is clearly a point of pride, but there will always be non-believers out there. It can be a tough sell, but Palank says you just have to be open minded.

“We hope others will at least try and understand why it’s so important to us,” he says. “It’s a Midwest thing.”