Eduardo Sousa and Diego Labourdette are an odd couple: Sousa is a jovial, fifth generation Spanish farmer. Labourdette is a soft-spoken academic - a PhD ecologist and migratory bird expert.

Together, they're in the foie gras business.

In 2013, Sousa and Labourdette teamed up to market a more ethical, sustainable way of making foie gras - i.e. high-fat goose or duck liver, a delicacy in Europe - without the controversial force-feeding its production usually requires.

Their method involves bamboozling wild geese who touch down in Spain once a year to gorge themselves on acorns and olives, before flying south for the winter.

Migratory bird expert Diego Labourdette and farmer Eduardo Sousa at the latter's farm

Sousa and Labourdette have since become darlings in the culinary world. "The market for foie gras is incredible! France makes millions of kilos a year," Sousa explained over the din of raucously squawking geese on his 1,200-acre goose farm in the Spanish province of Badajoz, about a five-hour drive from Madrid. "That's another world from what we do here."

Most foie gras production uses gavage - force-feeding - a brutal practice where tubes are forced down the geese's throats, and their stomachs pumped with more grain in a couple weeks than they would ever eat in a lifetime.

Their livers grow 10 times bigger than normal, with large deposits of fat - which is what makes foie gras so rich. The controversial practice is banned in at least 20 countries.

Letting the geese be wild

Sousa and Labourdette set out to commercially produce foie gras in a natural, sustainable way. Sousa said it's nothing new: it's actually the production method used in Spain more than 500 years ago, before the Spanish Inquisition.

Eduardo Sousa poses with a jar of the foie gras produced on his 1,200 acre farm in Badajoz, Spain

"In 1492, Spain expelled the Jewish family that lived on this land, and the church took their property," Sousa explained. "They used to raise geese on this land - 300 years later, my family bought it from the church, and we revived that Jewish family's tradition."

Walking over rolling green hills dotted with olive trees and oaks, Sousa calls out to his approximately 2,000 geese as if they were children. The geese roam free; they're not housed in coops.

Instead of force-feeding, the geese fatten themselves up naturally, doubling their body weight in just a few weeks, to prepare for their annual migration.

Wild geese spend the summer in northern Europe. Then they migrate south to Africa each autumn, Labourdette explained. "They stop here in Spain on their way, to eat and gain energy for the long flight. But lots of them never leave! Because they find such good habitat here."

Geese are adaptable, he says, and they eat whatever the environment provides. Foie gras from Denmark has a fishy taste, because the geese eat seafood there. Here in Spain, they feed on calorie-rich acorns, olives, figs and seeds.

Geese browse on the Badajoz landscape - and pick up the flavors of the countryside

The autumnal new-moon sacrifice

Unlike big commercial foie gras farms, where geese are slaughtered every few weeks for their liver, here it happens only once a year - usually in October - with the first chill of autumn, on the night of the new moon. Sousa calls it "the sacrifice."

"We paralyze them with flashlights. They become hypnotized when they're confronted with such bright light at night," he said. "It's an ancient practice. The birds seem like they're asleep. Then we sacrifice them with a knife. It happens very quickly, and they don't suffer," Sousa asserted.

Feathers are plucked for goose down. Some of the meat is cured, to make a goose-meat version of Spanish jamón (ham). And the goose livers are seasoned and boiled whole for about 20 minutes in glass jars - the same jars in which they're sold.

The flavor of the land

The farm's caretaker, Domingo Diaz Escudero, strums flamenco on his guitar as guests gather around a wooden table to sample last fall's batch. The foie gras is smooth, rich - with hints of all the wild herbs, olives and fruits the geese themselves have eaten in these mist-streaked hills.

"Songs have the smell and flavor of the land they're from, just like our geese," said Diaz Escudero, who was born and raised near Sousa's farm, and walks to work. "They're part of nature."

Sousa snacking on some goose liver at his crib in the hills of Badajoz

In 2006, this foie gras won the Coup de Coeur, a coveted French gastronomy award. The contest is like the Olympics for foodies. That caught the attention of a famous New York chef, Dan Barber, who visited Eduardo Sousa's farm and gave a TED Talk afterward.

"I went to Spain a few months ago and I had the best foie gras of my life," Barber said in the TED Talk. "The best culinary experience of my life. Because what I saw, I'm convinced, is the future of cooking."

Barber described the utter simplicity of how this foie gras is made. He called it transformative and sustainable. He also wrote about it in his latest book, The Third Plate. And Sousa's sales skyrocketed.

Celebrity goose farming

"This was always just a hobby for my family," Sousa said. "But ever since the visit of Dan Barber, I've started getting orders for my foie gras from all over the world."

He sells every gram of foie he makes - and there's quite a long waiting list, too. A small jar costs 200 euros, because it's produced only once a year from just 1,600 geese every autumn.

The modest scale of the kill allows for natural repopulation of the flock, and plenty of food for the geese who survive. Sousa takes only what nature allows.

Marín and Cabellon made a special trip just to sample Souza's foie gras

Sousa recently signed a deal with Celebrity Cruises to provide foie gras on high-end cruise boats. He has a website, but the only place you can buy in-person is a tiny storefront in a village near the Spain-Portugal border. One recent afternoon, the shop got some visitors from as far away as San Francisco.

"We watched it on TED Talks and then I made [my boyfriend] stop here on the way to Madrid," said American tourist Alegra Cabellon. "I'm really excited to see the product."

Cabellon takes a selfie with Eduardo Sousa, and buys several jars of his foie gras. She'll have to eat it before she heads home, though. Customs rules won't allow her to bring it into the United States.

This foie gras is sold, for now, in Europe only - but Sousa hopes he will be able to sell it in North America soon.