KANSAS CITY — From brioche to ciabatta, upscale buns are dressing up more drive-thru dinners.

The sesame seed standby isn’t cutting the mustard with millennial consumers, who crave premium fare found in fast-casual restaurants. As a result, fast-food chains are upgrading burgers and sandwiches with bakery-style bread.

Buns have moved from a supporting role to the spotlight at Wendy’s, which over the past year has launched a string of limited-time offers on ciabatta, brioche, pretzel buns and a multi-grain flatbread made with flax seeds, cracked wheat, rolled oats, millet and sesame seeds. The chain’s artisanal bread strategy is paying off. Wendy’s April introduction of Flatbread Grilled Chicken sandwiches led to the company’s highest level of large chicken sandwich unit sales in nine years, and the Pretzel Bacon Cheeseburger outperformed all other promotional hamburgers in recent Wendy’s history during tests, the company said.

Slideshow: Fancier offerings at fast-food chains.

Now, more quick-service chains are thinking outside the burger bun. Pretzel bread also popped up last year at Sonic Drive-In, Blimpie, Arby’s and several casual-dining chains like Chili’s and Ruby Tuesday’s.

“The pretzel bun is a real natural because it brings a lot of these cues of Old World to an already recognizable item,” said Kara Nielsen, a trend researcher at San Francisco-based CCD Innovation. “It has a deeper, darker flavor, and it has a little artisanal touch to it, even if it’s a manufactured product.”

Last November, Hardee’s and Carl’s Jr. debuted fresh-baked buns made with dough that is given time to rise before it is baked, cooled, sliced and served, resulting in a dense texture and sweeter flavor, according to the company. The new buns come standard on the chains’ premium burgers and may be substituted on other sandwiches for an additional charge.

And Subway this month announced a bread upgrade of a different sort: the sandwich chain said it plans to remove a controversial dough conditioner from its loaves.

As consumers increasingly consider the origin and authenticity of their food, items that appear handmade or healthier carry instant appeal.

 “Q.S.R. and fast-casual operators are looking to make standard items seem more interesting and unique and trying to create more competitive positioning of items without revamping the whole menu,” explained Maeve Webster, senior researcher at market research firm Datassential. “Changing the carrier is a fairly easy change compared to other changes you could make. It’s not necessarily disruptive to the back of the house from a cost or handling standpoint. And you can increase the price point because it has a more unique, artisan perception.”

Other chains are stepping up the sandwich’s sidekick. Fancier fries launched in recent months include sweet potato waffle fries from Jack in the Box, reduced-fat Satisfries from Burger King and Natural-Cut Fries at Sonic, which said the new skin-on french fries, made with whole russet potatoes, are crispier and fluffier than the chain’s original.

As far as bread trends go, expect to see more sprouted bread and ryes emerge as an extension of Old World-inspired fare.