Four years ago, the rise of extreme fast food had America on death watch. KFC had unleashed its Double Down burger--a monstrous concoction featuring endless gobs of bacon and cheese sandwiched between two boneless fried chicken cutlets--and IHOP was going all out with cheesecake-stuffed pancakes. Not to be outdone, Denny's unveiled its seven-item "Baconalia" menu, which included a bacon sundae. It was gross, and customers couldn't get enough of it. 

Mercifully, the trend of fast-food chains creating unholy food hybrids played out and Americans resumed their old (if still indulgent) eating habits. But then halfway through 2013, pastry chef Dominique Ansel got the inspiration for a new, more dignified mashup: He crossed a croissant with a jelly-filled donut, thereby creating the Cronut.

This wasn't your ordinary confection. Oh no, the Cronut was something entirely different. It immediately became a pop culture phenomenon, spawning a black market on Craigslist, endless satire, and even some knockoffs. (Ansel was so distraught by the latter, he quickly filed for a trademark to protect his creation.) Meanwhile, tourists continued to wait for hours outside Ansel's eponymous bakery in New York City's SoHo neighborhood, braving snow and arctic temperatures just for a shot at sampling the pastry. 

That was the beginning of the food mashup madness. The worst was yet to come.

Cheetos macaroons sprang up at the Macaron Parlour bakery in Manhattan's East Village, and Brooklyn cheese purveyor Valley Shepherd unleashed its large-and-in-charge Valley Thunder, a sandwich that comes loaded with cheddar cheese, brisket from Bubby's restaurant, and macaroni and cheese. Meanwhile, Ansel concocted the cookie shot, a shotglass made from cookies with milk. 

That entrepreneurs were behind this trend wasn't the least bit surprising. Food mashups are inventive, combine popular things, and challenge norms. If you think about it, says Robert Thompson, a pop culture professor at Syracuse University, some of the most enduring food staples started as mashups. 

"The hamburger was a mashup--ground beef used to be served on plates with gravy," he says. "The sandwich was a mashup, taking a variety of sliced meats and vegetables and constructing it in such a way that it can be eaten by hand." Even Italian-style pasta, which always struck me as being older than time itself, wasn't always served drowning in red sauce.

What's tough for small business owners these days is taking those hybrids from novelty to mainstay. "Every now and again one of these will come along and last for centuries," says Thompson, but "a mashup that actually makes it into the national cuisine, much less becomes a key part of it, is a tough thing to do." You certainly can't bank on being able to build a business around it. 

"There needs to be real value in there for customers and things require thought and finesse," Ansel says in an email interview. "Winning over hearts requires a genuine story. ... And it's never about cashing out on one product. It's about continuing to create as many products as we hope our customers will appreciate." 

Still, fast-food chains like Taco Bell, which released its waffle taco Thursday, are intent on trying to recreate some of that Cronut magic. The company, whose latest ad [below] features men named Ronald McDonald touting the virtues of Taco Bell's breakfast menu, is going all out to ensure the waffle shell stuffed with cheese, eggs, and sausage sets off a frenzy. 

For his part, Ansel says he'll be fine if his Cronut never goes mainstream. In fact, he'd prefer it that way. "It's a trademarked item and we do it here for the store," he says. "I don't believe longevity requires being mass-marketed. I believe in protecting the preciousness and sacredness of a little bit of creativity. And I hope that it'll inspire people to find true innovations beyond it."