(CNN) — You'd think a city as cosmopolitan as San Francisco would have better things to do with its Saturday morning than go all caramelized bananas over a muffin.
But wander past a nondescript shop front on Larkin Street in the city's Tenderloin district at around 7 a.m. and you'll see a group of people in the thrall of their latest foodie discovery.
So much so that that they're willing to line up for 90 minutes or more to get their hands on one.
Well, two, to be precise.
That's because the muffin in question isn't exactly a muffin -- it's a cruffin -- and because demand for the things at Mr. Holmes Bakehouse has been so great since its debut that owners have limited sales to just two per customer, so as not to disappoint their growing fan base.
You'd think they were selling Led Zeppelin reunion tickets.
"It's a myth of a pastry, it's the unicorn of pastries," says Ry Stephen, 28, Mr. Holmes Bakehouse co-owner and pastry chef.
"You can't seem to get it. You definitely have to wait in line."
It's been this way since the shop opened in a notoriously seedy part of town in November 2014 -- "This isn't Nob Hill, it's not typically where tourists would stroll around," says Stephen -- with early demand driven by a savvy social media campaign.
"It was a trip, the first morning it was pouring rain," says co-owner and entrepreneur Aaron Caddel, 23, who runs the business end of the operation.
"We were expecting no business -- this is a pretty ghetto part of town in the middle of the Tenderloin -- but at 7 a.m. there were 10 people waiting in line."
What's a cruffin?
San Francisco icons: Cruffin and Transamerica Pyramid Center.
A cruffin is a cross between a croissant and a muffin. It comes in the shape of a muffin, but the flakey layers of "laminated" (with French butter) brioche dough give it the pull-apart texture of a croissant.
The cruffin is based on an old French pastry -- Stephen didn't invent the cruffin, but he does claim to have brought it to San Francisco -- and requires a labor-intensive process of rolling and cutting dough over and over.
"It's 80% technique," says Stephen, who spent countless trial-and-error hours perfecting his own.
Cruffins at Mr. Holmes Bakehouse are filled with a different flavor each day.
You never know what you'll get -- s'mores, strawberry milkshake, peppermint, caramel cream.
After apprenticing in his native Melbourne, Stephen spent two years working in a pastry shop in Paris before marrying an American and relocating to San Francisco, where he met California native entrepreneur Caddell. His kitchen talents stretch beyond the cruffin.
Mr. Holmes Bakehouse -- the name comes from one of Stephen's mother's two cats, Sherlock and Holmes -- draws crowds for its other concoctions.
"No one does a donut like we do," says Stephen.
He makes his with flavors like vanilla cheesecake, passion fruit curd, caramelized banana and strawberry cream.
Other popular items include an outstanding cookie made with caramel, chocolate and cocoa nibs and the California croissant, which is stuffed with smoked salmon, pickled ginger and wasabi and comes with a packet of soy sauce.
Mr. Holmes Bakehouse co-owners Aaron Caddel (right) and Ry Stephen bask in the glow of their shop's neon popularity.
The third partner, designer/co-owmer Aron Tzimas, 28, another Australian, is responsible for the gleaming white look of the business, which has also attracted fans.
Tzimas conceived everything from the "I Got Baked in San Francisco" pink neon sign inside the shop -- it's not exactly the Golden Gate Bridge but it's becoming a "must pose" backdrop for Instagrammers -- to the elegant carry-out boxes that have also become a sensation.
Tzimas' box was inspired by the design of the rich packaging at the fictional Mendl's Bakery from Wes Anderson's "The Grand Budapest Hotel."
"I wanted this box to be like a gift," says Tzimas. "People are collecting them, stacking them in their houses."
Like Stephen, Tzimas' detailed approach to his end of the business has inspired what's starting to look like a cult following.
He confirmed this one recent Saturday morning while looking outside at another excited crowd lined up literally around the block.
"What we have here, this is not normal," he said.
Mr. Holmes Bakehouse, 1042 Larkin St., San Francisco; +1 415 829 7700; opens at 7 a.m. Monday-Friday, 8 a.m. Saturday-Sunday, closes when items are sold out; cruffins come out at 9 a.m. daily and had run out by noon on the Friday and Saturday CNN visited, though other items remained.