Baqar Taihan is digging for edible treasure.

In Ganish, an old Silk Road stop high in the snowcapped mountains of northern Pakistan, Taihan is overseeing the exhumation of a valuable stash of fatty gold: ingots of cow and yak butter, packed inside casings of birch bark, that have been buried for years beneath paving stones of the village square. Some of the cached butter is older than middle-aged Taihan himself.

“Our grandparents say we used to bury it for up to a century,” Taihan, a local community activist and an amateur historian, says. “Today the oldest butter I know of is only about 40 or 50 years old.”

Maltash, as the cakes of the tallow-like dairy product are known, are a delicacy in Ganish and the surrounding region of Hunza, a once independent kingdom that was annexed by Pakistan only in 1974. Guarded by 25,000-foot peaks and cut off for centuries from the outside world, the former statelet maintains an identity distinct from the rest of the country. Its yak herders and apricot farmers, most living in a hundred-mile-long river valley, belong to moderate Shiite sects and still practice elements of their pre-Islamic culture, such as wine making and shamanism. Unlike the spicy diet of much of South Asia, their cuisine is a light menu of grains, half-cooked vegetables (firewood is scarce in the alpine region), fruits, and fresh dairy products that, for its wholesomeness, has earned the people of Hunza a reputation for longevity.

And then there’s maltash.

“The [butter] here, like all that was given to us in the valley, was of the consistency of cheese, and had a most unpleasant odour,” wrote E.F. Knight, a British colonial officer who encountered the pungent food on a military expedition against the tiny kingdom in 1892. “The older this...butter is, the more is it to the taste of the highlanders. They bury it in the ground, and it is often kept there for generations until it is used, one hundred years being quite an ordinary age for Hunza ghee. These people like their butter to be stale and their wine to be new, and no doubt would consider us as coarse barbarians were they aware of our exactly opposite preferences.”

Maltash’s pungent smell is due to fermentation.

As the butter curdles over time, acidity inhibits bacterial growth, giving it an enormously long shelf life in an age before artificial refrigeration. Curing butter this way isn’t unique to Hunza. Moroccans preserve a softer form of butter called smen the same way. And turf cutters in Ireland still regularly turn up “bog butter”—muddy lumps of rancid butter, some up to 5,000 years old, stashed by long-forgotten ancestors in peat bogs. The last hunk of butter likely was buried in Europe in the 19th century, but in Hunza thousands of pounds of it are still being stockpiled in the landscape—and eaten, usually with a hunk of flatbread.

“About 10 or 12 families have rights to bury their butter here,” Taihan says of the caches hidden under the prestigious real estate of his ancient village courtyard, where the cakes of emulsified fat, water, and air age slowly, two feet deep in cool soil. Each family’s supply, whether 10 or 50 years old, is marked by a colored piece of cloth under a flagstone.

“It’s not something we eat all the time,” Taihan says. “It’s a special food. We give it away at special events like weddings.”

He picked open the bark wrapping of one decade-old cake. It was hard as lead. It tasted of sour candle.