An 85-year-old tavern in Chicago is famous for paper-thin burger patties, an unlikely mascot, and an SNL skit

• We visited Billy Goat Tavern in Chicago, Illinois to see how they make their legendary cheeseburgers.
• The Chicago restaurant has been an underground oasis for politicians and journalists for 85 years.
• Billy Goat burgers are made with kaiser roll buns and thin beef patties.
• Visit Insider's homepage for more stories.

Following is a transcript of the video.

Narrator: Chicago is home to plenty of burger spots, but few can call themselves an underground oasis for politicians, celebs, and journalists. Over 85 years, this restaurant has evolved into one of Chicago's most iconic culinary landmarks. And although it's hidden beneath the city's bustling Michigan Avenue, it's become a required stopping point for both hungry locals and visitors.

Customer: It's 'cause of the history here. Places like these are hard to find. Good old mom-and-pop shops, you know, with old-culture food. And nothing's changed. The food, for years, has been the same here.

Narrator: This is Billy Goat Tavern, and it's been cooking up its legendary Cheezborger since the 1960s. Step inside Billy Goat Tavern, and you're instantly overwhelmed with its history. The underground shop is covered in a collage of news clips, pictures of celebrities and politicians, and, of course, notes of high praise for its legendary Cheezborger.

Sam Sianis: Cheezborger, Cheezborger, Cheezborger!

Billy Sianis: Cheezborger-Cheezborger. Double is the best.

Narrator: Billy Goat's burger is sandwiched in between two halves of a kaiser roll bun. In between the bun is a juicy, thin slab of fresh, all-natural beef and two slices of cheddar cheese.

Billy: We get deliveries of burgers every day, so we make them fresh every day.

Narrator: That's second-generation owner Billy Sianis.

Billy: And then we get fresh bread every day, kaiser roll. We toast this on the grill. So we just wait, you know, till they start to sweat, basically. Then you flip them. It's gonna be a nice sear, and that gives it the flavor. We put cheese on there. And these are the doubles, and you can make triples as well. But this is why we do a thinner patty, because you can do different-size burgers.

Narrator: To make for a more mouthwatering experience, Billy always recommends getting a double cheeseburger. Customers can choose whether to pile their burger with pickles, onions, or other toppings, but don't expect any lettuce or tomato.

Billy: Well, we say the goat ate all those, the lettuce and tomato, so we don't have any of them.

Customer: Bread is really good. The pickles, relish on there. I like that you can throw your own toppings on there. Really good.

Customer: It's very delicious, and the meat is fresh.

Narrator: Billy says the meat of a Billy Goat burger is made from a clod and chuck blend, which comes from the shoulder area of a cow. Billy's father and his great-uncle didn't want any filler meat and wanted to sell just pure beef. And the reason they kept their patties thin?

Billy: And it was because we wanted to sear it, but also be juicy inside. You do that when you cook it fast. Also, you could stack it using a leaner ratio. It cooked better and it stayed the same size, it didn't shrink too much. So that was the ratio that they liked, and we've been using that ever since.

Narrator: But selling quality cheeseburgers isn't the only reason this tavern became a Chicago institution. The original Billy Goat Tavern was born in 1934 across from the Chicago Stadium, now known as the United Center, when William purchased the Lincoln Tavern for only $205.

Billy: After a few months of being open, a goat fell off a truck and landed in front of the door, and [William] brought it in as the customers came in, and he saw the reaction of the people, they liked it, and so he decided to keep it, and he used that as a mascot.

Narrator: From then on, William was known as Billy Goat. He adopted the goat, grew a goatee, changed the name of the bar to Billy Goat Tavern, and made the goat part of his business.

Billy: He started taking the goat to different events. Across the street was the Chicago Stadium, so he used to take it to political events, sporting events. He used to hide the goat in, like, a suitcase or something.

Narrator: Billy Goat's stunts continued to grant him local fame, and in 1964, he moved his tavern to where it is today: underground, right in the middle of the city. The tavern has since expanded to eight locations across Chicago.

Sam: Cheezborger, Cheezborger, Cheezborger! No fries. Chips! No Pepsi. Coke!

Narrator: That's Sam Sianis, nephew of "Billy Goat" Sianis, who's still yelling out their iconic catchphrase.

- Cheezborger, one Pepsi, one chip.

- Cheezborger!

- Pepsi, chip!

Billy: Back in the '60s, my dad and other cooks were mostly Greek. Some of them came straight from Greece, they didn't know a lot of English, so what they first learned was what was on the menu. So when a customer comes in and they place the order, they yell out the order. "So, what'll you have? Cheezborger, next. Cheezborger, next. Cheezborger, Cheezborger." And it sounded like you were getting yelled at, but they were just telling you what was on the menu.

Narrator: Billy Goat's catchphrase became so well loved by its customers that "Saturday Night Live" writer and Billy Goat regular Don Novello turned it into a popular sketch on the show's third season.

- Cheezborger, Cheezborger, Cheezborger, four Pepsi, two chip.

Narrator: From then on, Billy Goat gained national fame and even received high praise from food icon Julia Child.

Julia Child: That's delicious. That's very good.

Customer: It's an institution of Chicago. It's a great place to be.

Billy: This place feels like home, so it's not anything, like, different, but you appreciate that people recognize the place and they come here to eat and have a good time.

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