Who invented Kiwi Onion Dip, and why isn’t there a gold statue of that person on top of Mt Cook? Hayden Donnell goes on a wildly emotional search for an unheralded New Zealand genius.

The woman on the other end of the phone line sounded theatrically English, like a Radio New Zealand newsreader from the 1950s. It was the voice of someone who’d cackle as she topped up your glass of sherry after an episode of Midsomer Murders. She was likeable. Mischievous. She was also meant to be dead.

“Hello, it’s Rosemary Dempsey speaking,” she said.

I had been searching for a criminally unsung New Zealand hero. Someone who has helped define the New Zealand summer; who may be our greatest alchemist. But while Ernest Rutherford is on the $100 note, this person has been left to languish in obscurity. I’m talking, of course, about the inventor of Kiwi Onion Dip.

Our disregard for the dip’s architect has bugged me for years. Every time I’ve bitten down on a dip-drenched chip, I’ve wondered the culinary savant behind the flavour miracle being performed in my mouth. Friends and loved ones have often heard me exclaim “Whoever invented Kiwi Onion Dip needs an urgent knighthood”. Late last year I decided to act on my convictions, track down my idol, and try to win them the respect they deserved.

I began where all searches for truth begin: Yahoo Answers. It attributed the invention to the Earl of Sandwich. That proved to be false. I went to Nestlé, which produces the reduced cream and onion soup that combine to create the dip. Its spokeswoman, Margaret Stuart, passed on many promising leads. The first recorded recipes for the Kiwi Onion Dip were printed in pamphlets from the early 1960s. All of them gave credit to the woman in charge of the company’s test kitchen. Her name: Mrs Rosemary Dempsey.

But Stuart’s reply to my request for further information about Dempsey left me bereft.

“We understand she is no longer alive,” she said. “She never married and had no children, so any living relatives would not be close.” It was cold in its certainty; brutal in its formality. There was no hope. No point looking. Rosemary was gone.

There was only one place to turn: the spirit realm. I rang an experienced psychic. Unfortunately, for compelling legal reasons, I’m not able to reveal anything about my expensive 15-minute interaction with the dead. However I did come away convinced of one thing: Dempsey’s ghost favours adding vinegar to the dip, rather than the more popular splash of lemon.

In desperation, I turned to the only power greater than death: Mark Zuckerberg. On the morning of January 7, I posted a Facebook status pleading for help. Thankfully the algorithm’s eyes shone kindly on me. My post was shared 61 times, including on historical enthusiasts society Old Auckland and apostrophe-loving public relations collective the Kiwi Journalists Association. I was directed to Helen Leach, an Otago University food historian. She had old recipes from Dempsey but few biographical details. I went to see New Zealand cooking icon Tui Flower at her Mt Eden home. She’d seen Dempsey at parties 30 years ago but hadn’t kept up with her.

My leads fizzled out. A week later I was phoning random elderly women with the last name Dempsey in Hamilton. During a lengthy conversation with a pensioner, an email came through from a woman named Lisa Varga.

“Hi Hayden,” it read. “Did you find Rosemary Dempsey? Her married name is Mount… Rosemary is my Grand Aunt. Didn’t know about the Kiwi Onion Dip – what a family claim to fame!”

Nestlé was wrong.

Rosemary was alive.

The retirement village where Dempsey lives is in on a leafy street in the Auckland suburb of Epsom. Her small apartment is filled with antiques. A grandfather clock. An old dining set. A jar filled with a five-year-old liquor of unknown variety and origin. There’s a perfectly kept garden outside. Dempsey is 85, but she does yoga on Thursdays, and remains a committed member of her local walking group.

She greeted me with the voice I recognised from her call two days earlier. “I was told you wanted to speak to me about that dip I invented, wow, it must be, 55 years ago,” she’d said then. Overwhelmed by joy, I’d made a whinnying sound like a sick horse and booked an interview.

I was a little calmer in person. We sat down at the kitchen table and Dempsey told me the story of how Kiwi Onion Dip was invented.

It began when she was freelancing as a home economist in the late-1950s. A call came from Nestlé’s New Zealand office. She was offered a job heading up the company’s fledgling test kitchen. Her role was to come up with recipes that used Nestlé products in an effort to increase their popularity.

Every month, AC Neilsen would deliver a presentation on how products were selling. About a year into her job, Dempsey heard onion soup was sliding down the charts. “We needed to do something to boost those sales,” she said. “And it was a challenge. I really enjoyed a challenge. So, back to the test kitchen.”

It was the early 1960s and dip was on the rise. People were laying it out on tables at cocktail parties. Dempsey decided to see whether she could insert onion soup into the fad. She went through the company’s products trying to find a good mixing ingredient to mix it with, instinctively favouring creamier flavours. Her Eureka moment came when she tried one of Nestlé’s more obscure products – reduced cream. “I mean, if you mixed onion soup and fresh cream you wouldn’t get that flavour,” she said. “And so it was a matter of trying [reduced cream] out, and it worked. It worked very well.”

That moment changed the course of New Zealand history. Dempsey’s creation spread like a virus through the social circuit, quickly becoming the dip of choice for everything from barbecues to baby showers. Its popularity endured more than five decades. Norman Kirk died. Rob Muldoon came and went. There was a global financial crisis. Then another one. Kiwi Onion Dip remained. “From then on whenever I went to the AC Nielsen presentations I was only interested in onion soup. It was so exciting to see the sales growing and growing and growing,” Dempsey said.

Nestlé made millions and millions of dollars out of the recipe. Dempsey never profited. She eventually left the company, going on to become the Herald’s cooking section editor for many years, before travelling the world, raising two children, retiring, and finally settling down in Epsom.

For nearly 50 years, Dempsey barely thought about the Kiwi Onion Dip – until her sister called in 2005 saying she’d heard her name on Newstalk ZB. Nestlé had put out an ad celebrating 120 years of operations in New Zealand. It credited Dempsey as the inventor of Kiwi Onion Dip. She decided to call the company to complain.

“I thought, well I don’t know anything about this. I know nothing about this at all. So then I rang them and said I rather thought they should ask permission to use my name.”

Dempsey said her calls went to several people at Nestlé New Zealand, including the general manager’s secretary and someone who she thought was a lawyer. She never got the company’s manager on the phone, and eventually gave up after being given what she thought was an insulting compensation offer.

“At that time my husband was very ill. And I thought ‘no, I don’t need this. I’ve got enough to think about and do.’ So I just left it. And I did say to them I felt that they should recompense me, and they offered me a basket of their ‘fine Nestlé products’. Which I refused. I rather felt it was not quite right,” she said.

She still feels disappointed at the exchange.

“Obviously it’s not very good. They didn’t want to know me. They did not want to know me.”

That was roughly 10 years ago – not long enough for the incident to have slipped out of the company’s institutional memory. So why was Nestlé telling me Dempsey was dead, that she’d been a lifelong bachelorette, and had never had children?

I went back to Stuart to inform her of Dempsey’s continued existence. “That’s great!” she wrote. Her earlier reports about Dempsey’s lonely demise had been based on bad information, she said. “There was certainly no intention to deceive,” she said. “That came internally through everyone just saying ‘she died’. I suspect that something one person thought just took on a life of its own.”

Stuart said there was little in the company’s records about Dempsey’s complaint. “I tried to find out about any contact with Rosemary Dempsey around the 2005 project. Apart from the actual ad itself, this was not very productive.”

Now Nestlé knew Dempsey was alive, would it recognise her as a company icon and offer some payment? Stuart didn’t want to commit to a reward.

“Actually I’d like to do something like that,” she said. “What it comes down to is we’ve got something on at the factory in a few weeks time that we’d love to invite her to.” She wouldn’t tell me what the event was. “It’s not unrelated [to Kiwi Onion Dip],” she said.

Even if it Nestlé doesn’t hail Dempsey as a New Zealand hero, we should. Professor Leach, who’s been hailed as the “gatekeeper of our gastronomic past”, agreed Dempsey’s achievements should be recognised by both Nestlé and New Zealand. Lauraine Jacobs, a food writer and columnist for The Listener, said Kiwi Onion Dip was an “all-time classic”. “My mother made it. My son and his wife make it, and think themselves clever. So now it is the darling of yet another generation.”

Dempsey’s dip has created more enduring joy than Richie McCaw. Cured more social ills than Nigel Latta. Enriched more lives than Suzanne Paul. It’s as Kiwi as pavlova, as much a part of our national identity as jandals or ‘Slice of Heaven’.

But don’t take my word for it. Look to your own history. How many of your defining culinary experiences do you owe to Rosemary Dempsey? Your most memorable birthday: the dip was there. Your wedding: the dip was there. Your funeral: the dip will be there. Kiwi Onion Dip has been with us through the best of times and worst of times. While people fail, the dip stays true.

It’s a national shame that we’ve let its inventor spend her life unremarked and unmentioned. Dempsey deserves a spot in the Kiwi pantheon, between Phar Lap and the Briscoes Lady. There should be a plaque with her name on it in every restaurant. One of her dip-mixing forks should be placed in Te Papa. Bill English should issue a statement praising her achievements. At the very least, Air New Zealand should gift her flights to see her daughter and granddaughter in Boston.

At least that’s what I think. Dempsey herself is happy to stay out of the spotlight, just like all true Kiwi legends. Sometimes she’s tempted to ponder what could have been if she’d somehow kept 0.01% of the dip profits. But mostly she reflects on her luck: to have had a good family, rewarding work, and to have brought joy to thousands of people.

“I’m happy as I am,” she said. “I have a wonderful life.”