Dunkin': Croissant Donut permanent

A concept that once sounded downright flaky has become a humongous hit.

Dunkin' Donuts announced on Wednesday that the Croissant Donut -- which was supposed to be a limited time only offer -- has been added to its permanent menu.

Never mind that Dunkin' was hardly the first to sell the baked blend of croissant and doughnut that looks like a glazed donut but is baked with a flaky, croissant ring.

But it won't be the last.

Since Dunkin' rolled out the then-limited-time item in November, it quickly emerged as one of the most successful limited-time bakery items in the brand's history, says John Costello, the chain's president for global marketing innovation, in a statement.

The numbers are staggering. Dunkin' has sold some 8.5 million Croissant Donuts since November. Because of that enormous consumer interest, says Costello, the brand will start to expand the Croissant Donut platform in 2015.

For example, In March, a Boston Kreme Croissant Donut -- filled with Bavarian Kreme and drizzled with chocolate icing -- will be available at some stores in New Jersey.

But this is about more than croissant doughnuts. "What is really going on here is the democratization of the mash-up food concept," says Tom Vierhile innovation insights director at DataMonitor Consumer, a consumer research specialist. The trend may have originated in specialty bakeries, but has now gone well beyond that, he says.

While the initial hysteria around the Cronut has abated, the broader hybrid food trend is relatively new and gives fast-food restaurants a way to lure consumers -- particularly younger folks in search of new flavors, says Vierhile. For example, IHOP recently added Criss-Croissants – a croissant baked in a waffle iron – as a limited time offer.

Meanwhile, flavor mash-ups aren't going away any time soon. They are so hot, says Vierhile, that Datamonitor Consumer named "mash-up mania" one of its top ten trends to watch in 2015.

Dunkin's Croissant Donut weighs-in at 300 calories, 14 grams of fat, 20 millgrams of cholesterol and 230 millgrams of sodium, according to Dunkin's nutrition chart.

But the original Cronut, a croissant-doughnut hybrid, was invented by a New York City bakery chef, Dominique Ansel, and launched in May, 2013. It's sales took off and the concept went seriously viral. Today, bakeries across the world are making croissant doughnut combos.

But Ansel, who created the Cronut, isn't sitting on his laurels. In honor of something dubbed International Pancake Tuesday, the pastry chef has linked-up with Nutella and created another talker: the Nutella Pancake Cone.