KANSAS CITY — A cheeseburger on Jack in the Box’s new late-night menu is topped with pickles, tomato, lettuce — and a sourdough grilled cheese sandwich.

Billed as a “munchie meal,” the Stacked Grilled Cheese Burger is merely the latest in a string of over-the-top launches from chain restaurants this year.

From a peanut butter and bacon milkshake to a bacon and egg sandwich on a halved glazed donut, extreme items on mainstream menus meld sweet and savory, novelty and indulgence.

Click here for a slideshow of extreme eats on mainstream menus.

Mary Chapman, director of product innovation at Chicago-based Technomic Inc., dubs them “shock foods.”

“People are going to order it because it’s fun and funny, but it’s not something that someone is going to order once a week,” Ms. Chapman said. “Restaurant chains put things on and take things off all the time, and so why not put something on that’s really crazy?”

While some kitschy items remain on menus for a limited time, others become core fixtures, even hot sellers. Take the Doritos Locos Taco, the taco-tortilla chip hybrid that has become Taco Bell’s most successful product launch with more than 500 million sold.

Adventurous eating may be the result of economic recovery, according to food trend experts.

“Right now, we’re headed more toward experimental, exotic, adventurous, courageous,” said Suzy Badaracco, president of Culinary Tides, an Oregon-based market research firm. “We’re feeling better about the economy. We’re brave; we want to try new things.”