In Palm Springs, California, the date shake is the perfect foil to the resort town’s desert heat: a sweet, chilly treat with surprisingly complex flavours.

I placed my order and the teenage clerk sprang into action, scooping vanilla ice cream into a plastic cup. She slathered it with caramel sauce and spooned in chunks of fruit. A blender whirred, and less than a minute later, she handed me a beverage towering with whipped cream.

This was the moment I had anticipated for years. I had come to Palm Springs, about 100 miles east of Los Angeles, lured by tales from California friends of an incredible milkshake made with locally grown dates. The drink they described was the perfect foil to the resort town’s desert heat: a sweet, chilly treat with surprisingly complex flavours.

The date shake is one of the culinary triumphs of old California

Food writer Michael Stern, who has been chronicling US regional cuisine for nearly half a century, counts himself a fan, calling the shake “one of the culinary triumphs of old California” And in April, blenders have been working overtime, as revellers drawn to the famed Coachella Valley Music and Arts Festival order the drink in droves.

But when I took a sip, something wasn’t right. It was good, certainly, but not a drink to inspire legends. It was too sweet, with a chunky consistency of unblended fruit. Had I been misled? I stepped out of the chain ice cream parlour, the only seller I could find open at that hour, and into the warm desert night, wondering if it all was hype.

You may also be interested in:
• A 4,000-year-old yoghurt
• The dessert that’s blocked at borders
• A rare cake that’s cooked on a spit

The shake certainly has a long history, emerging more than 80 years ago at the intersection of Hollywood glamour, agricultural innovation and tourism promotion. It’s a largely unsung piece of Americana that’s enjoying a bit of a resurgence, thanks to health-food trends playing up the nutritional benefits of one of the world’s oldest cultivated tree fruits.

It's one of the best things I’ve ever put into my mouth

While there’s some debate, the shake was likely invented by Russell Nicoll, who in 1928 became one of the first in the Coachella Valley to see the tourist potential of a date shop. According to an article in True magazine in the mid-1940s, he had heard that some nomads in the Middle East lived entirely on dates and goat’s milk, which inspired him to experiment with a dairy-based beverage himself. The (cow’s) milk shake he concocted immediately won rave reviews across the Western United States. A newspaper columnist in Salt Lake City, Utah, even offered a prize to the reader who could best describe the delights of the beverage.

Other entrepreneurs were soon blending their own version, and the drink’s reputation has never faded. A few years ago, when British celebrity chef Jamie Oliver compiled a cookbook on classic American cuisine, he made sure to include a recipe for what he called ‘The Amazing Date Shake’. Seattle food writer Braiden Rex-Johnson is more to the point, calling it simply “one of the best things I’ve ever put into my mouth”.

So I still had hope the next day when I walked into Shields Date Garden, a grower and decades-old tourist attraction with a 40ft knight pointing to the entrance. Signs promised free samples as well as continuous screenings of a documentary with the lurid title The Romance & Sex Life of the Date.

Even on a weekday, the carpark was packed. Maybe this shake had legs after all.

I wandered into the sprawling gift shop that offered an endless variety of dates and date products – cakes, jams, bars, rolls, cookies, pies, bread, butter, paste, sugar – and found my way to a small auditorium showing the film. It told an inspiring American success story.

At the turn of the last century, the US Department of Agriculture sent plant explorers on a global search to find new crops suitable for North America. They brought back date palms from North Africa and the Middle East that local growers like Bess and Floyd Shields quickly learned would thrive in the Coachella Valley. On one trip to a Moroccan oasis, explorer Walter Swingle obtained six offshoots that today account for all the medjool dates grown in the US.

All this history was a lot to absorb, and I still hadn’t tried another milkshake. Wary from the previous night, I stalled, first heading to Shields’ palm-shaded courtyard restaurant for another regional specialty: chopped dates, blue cheese, walnuts, pears and dried cranberries over spinach. It was tasty, but who was I kidding? I hadn’t come this far for salad. Finally, I wandered back into the gift shop and settled on a stool in front of a counter where shakes had been served since before I was born.

A uniformed waiter grabbed a paper cup pre-filled with ice milk, a frozen dessert lower in fat than ice cream, topped it with milk, and spooned in a paste made with date crystals, a concentrate invented by the Shields in 1936. Then she placed the cup in one of the six constantly whirring blenders. A minute later, she handed me the 24-ounce beverage, and I took a tentative sip.

Wow. Earthy and sweet, it tasted of butterscotch, caramel and even chocolate. The drink was delicious.

Shields employee Jessica Duenow told me the secret is the ice milk, which lets the fruit’s natural flavours and sugars take top billing. “Dates are already very rich. To use ice cream would put it over the top,” she said.

But the region’s date industry was never about subtlety. The business blossomed about the same time as Hollywood. The Valley’s barren mountains and graceful palms proved to be an easy substitute for the Middle East, providing the setting for the 1921 film The Sheik, starring Rudolph Valentino. Other movies, with names like Sahara and The Veils of Baghdad, followed.

Locals played up the exotic connection, bestowing names like Mecca, Desert Camp and Oasis on their tiny settlements. In the 1920s, the town of Indio launched a date festival, and the fairgrounds, located at the corner of US Highway 111 and Arabia Street, still sports faux desert castles topped by minarets. Even today, the February event includes an Arabian Nights musical and the Queen Scheherazade Scholarship Pageant. It also offers camel and ostrich races – and plenty of shakes.

Across the Valley, kitschy shops and billboards recall holiday travel before the superhighway era. It was a time of cheap petrol and open roads, when the promise of an exotic roadside attraction and a gift shop could entice motorists to make an unscheduled stop.

The legacy lingers elsewhere, too. At Coachella Valley High School, a moustachioed mascot called the Mighty Arab lords over the gymnasium. (Its teams were once known simply as the Arabs, but the name proved too controversial and was changed in 2014.)

The school isn’t far from one of the region’s oldest growers, Oasis Date Gardens, which makes its shake with ice cream and organic fruit that has been baked and blended into a paste. It was thicker than the others and served with a spoon, but just as memorable. “You get something very sweet, and very strong, like honey,” said Francisca Reyes, who made my drink. “You don’t get tired of them.”

You don’t get tired of them

I left the shop with newfound curiosity about the graceful palm. Growing dates, I’d learned from Shields’ film, is not a simple matter. Groves are planted with one male tree to about 50 females per acre, and nothing is left to chance. Workers harvest pollen from the males to hand-fertilise female flowers.

The job, traditionally performed by employees called palmeros, is difficult. An exhibit at the Coachella Valley Historical Society’s Date Museum displays the mesh saddles workers once used to hang from trees. Even now, with ladders and lifts, it’s dangerous work, and growers are having trouble recruiting a new generation to learn the trade, which requires climbing each tree more than a dozen times a year. “Everything is still done manually,” said Nancy Cohee, who leads agritours in the area.

But what a payoff. At the end of a good season, one tree can produce up to 300lb of the nutritionally dense fruit. No wonder there seems to be a shake shop on every corner.

My tasting tour continued at Hadley Fruit Orchards, which welcomes customers in the town of Cabazon near the Valley’s entrance. Here I was served a soft-serve machine shake that would have wowed me if it had been my first. The menu also offered date shakes mixed with banana and mint, but that seemed like overkill.

Indeed, this desert dessert diet was taking its toll. With a little less spring in my step, I headed to King’s Highway diner to try a creamy offering made with vanilla bean gelato. Then at the swanky Miramonte Indian Wells Resort and Spa, executive chef Paul Hancock served up a boozy shake laced with dark rum.

“It has chocolate and caramel undertones, all those velvety luscious flavours,” he said.

One of my last stops was a vegan offering at Nature’s Health Food & Café, and, to be honest, my expectations were low. But when I took my first sip of the ice-soymilk shake, I was astonished. It had the same intricate taste as at Shields, and was just as satisfying.

Had I found a secret elixir? A dessert I could enjoy every day without ballooning to the size of an overfed camel?

I turned to a woman in a tie-dyed T-shirt behind the counter. Was this shake, I wondered, low in calories?

She smiled and shook her head. No, she told me, absolutely not.

Join more than three million BBC Travel fans by liking us on Facebook, or follow us on Twitter and Instagram.

If you liked this story, sign up for the weekly features newsletter called "If You Only Read 6 Things This Week". A handpicked selection of stories from BBC Travel, Capital, Culture, Earth and Future, delivered to your inbox every Friday.