Not so very long ago, restaurants that menued milkshakes had all of their bases covered if they offered the three traditional flavors: vanilla, chocolate and strawberry. But times have changed — and dramatically, too. Today, it's not unexpected to hear about ice cream-based milkshakes flavored with jalapeño peppers, salted caramel, Oreo cookies, Jack Daniel's Whisky or even an entire 3-inch pie.

It's pretty much anything goes, in fact, in the changing world of milkshakes — and the more innovative the better, experts say. “Milkshakes are an indulgent treat,” says Dennis Lombardi, executive vice president-foodservice strategies for WD Partners, a design and development firm in Columbus, Ohio. “And we're seeing more restaurants going beyond the traditional flavors. They're a great way to extend a restaurant's menu.”

In addition to satisfying the consumer's indulgence for a sweet treat, milkshakes also offer the benefit of being highly portable — an important generator of sales at many foodservice operations. “Milkshakes are more portable than a cone or a cup of ice cream,” Lombardi says. “It's something you can eat while driving.”

According to Datassential, the number of milkshakes found on restaurant menus slipped by about 2 percent from last year. However, the menu research firm says almost one in five restaurants across the country still offer milkshakes. And while top-selling flavors include peanut butter, coffee, caramel, orange and Oreo, an increasing number of operators are finding a more adult market by spiking them with some form of alcoholic beverage.

“As an alternative, [spiked milkshakes] can be a fun menu addition to a full-service restaurant with a liquor license,” Lombardi says.

However, he advises, while milkshakes can help to drive revenues, they require some additional labor, too. “The challenge is to what extent will a hand-dipped milkshake impact the speed of service,” he says.

The addition of milkshakes at the Jack Daniel's Club in Globe Life Park, the home of the Texas Rangers in Arlington, Texas, has helped boost sales, according to general manager Jodie Haifley. Operated by Buffalo, N.Y.-based Delaware North Sportservice, the club offers five alcohol-based milkshakes for adults and five nonalcoholic shakes for kids.

The thinking behind the milkshake launch was that management wanted to find a way to lift dessert sales — and transportability was an important component in the sprawling 48,000-seat ballpark. “We decided that we could create desserts in the form of milkshakes, which could then be brought back to the seats,” Haifley says.

The Jack Daniel's Club offers five adult milkshakes, the best-selling of which is Bananas Foster. To prepare it, bananas are first flambéed with brown sugar, butter and dark rum, and then folded into the ice cream milkshake together with banana liqueur and more dark rum. It is topped with whipped cream and sold for $12.95 in an acrylic tumbler printed with the Rangers' logo.

Other adult selections include a Grasshopper, with mint chocolate chip ice cream and crème de Menthe; Brandy Alexander, vanilla ice cream, cinnamon vodka and brandy; and Mocha Bourbon, chocolate ice cream, Jack Daniels Old No. 7 and Kahlúa.

The kids' milkshakes also offer some unexpected flavors —without the alcohol of course. In addition to vanilla and chocolate, the club features a nonalcoholic take on its Bananas Foster recipe, as well as a Cookie Monster shake, with cookies-and-cream ice cream, and Oreo cookie crumbs. A Caramel Praline shake is prepared with vanilla ice cream, caramel syrup, almond extract, cinnamon and whole milk. Kids' shakes sell for $8.95.

While originally introduced as a trial, Delaware North expects to not only keep the shakes on the menu at the stadium, but the company may introduce them at other of their venues, according to Glen White, corporate communications manager for Delaware North Companies.   

Delaware North Travel Hospitality Services also offers adult shakes at its licensed Grindhouse Killer Burgers outlet at Hartsfield-Jackson Atlanta International Airport. Among the five selections abides El Duderino, a Kahlúa, Smirnoff Whipped Vodka and Coffee Shake that pays tribute to the cult film, “The Big Lebowski.” Shakes sell for $9.50 each.

Southern-flavored Hill Country Chicken in Manhattan also has succeeded in creating a signature liquid dessert in the form of its Pie Milkshake. Hill Country, which also has an outlet in Brooklyn, N.Y., specializes in homemade pies, fried chicken and french fries, but has received plenty of local attention by blending its 3-inch miniature pies with vanilla ice cream and milk until a drinkable consistency is reached. The Village Voice listed it as one of its favorite dishes in 2013, writing that it was like “a liquid pie á la mode.”

“We're definitely known for pies and fried chicken, but people do come in specially for our pie shakes,” says Hill Country's executive chef Elizabeth Karmel.

She says the restaurant offers dozens of homemade pies, but usually only one pie shake is available daily — although the restaurant will prepare a special shake if a customer requests it. Hill Country's most popular pie selection is the Cowboy Pie, which Karmel calls “a candy bar in a cup.” It includes milk chocolate, dark chocolate, butterscotch, pecans, coconut, and graham crackers.

“But there are lots of flavors available,” Karmel says.

One could say much the same thing about Sonic Drive-In's Summer of Shakes promotion, which the 3,500-unit chain is reprising after a successful run last year. Sonic's is offering 25 milkshake selections, made with real ice cream and featuring such flavors as Chocolate Covered Jalapeño, Cookie Dough and Salted Caramel.

Mackenzie Gibson, Sonic's director of culinary innovation, says the Chocolate Covered Jalapeño shake has attracted a lot comments from customers. The shake is made by hand-spinning diced jalapeño peppers with real ice cream, liquid ice cream and chocolate, and then garnishing it with a whipped topping and a cherry. “It's tasty,” he says. “It has a hint of heat and a little tart flavor.”

This is not the first time Sonic has tested the boundaries of milkshake making.

Last summer the brand offered a Peanut Butter Bacon milkshake. This year, however, the chain is combining peanut butter with Oreo cookies, which has been “a huge standout,” Gibson says. “Everyone loves it.”

Other selections include Coconut Cream Pie, Strawberry Cheesecake and Oreo Caramel.

As a late-day incentive, the shakes are available at half price after 8 p.m. throughout the summer.

Gibson says the creative shakes appeal to customers who are feeling adventurous, although many decide they just want a traditional chocolate shake, depending upon their mood. “It's split,” he says. “We see the more flavorful and unique shakes selling as well as the classics.”

Meanwhile, the trend toward offering more adventurous ingredients in milkshakes “is one Sonic feels comfortable with,” Gibson says. “We're excited to continue to focus on unique flavors. Our customers expect that.”