Nordic wayfarers hadn’t been in Iceland for long when they realized trees were an unsustainable resource. In the 9th and 10th centuries, settlers quickly depleted the supply of birches and willows that speckled the countryside until firewood became rare. Luckily, these early explorers had brought along a renewable fuel source: the sheep they reared to survive. Now, in addition to harvesting sheep’s meat and wool, Icelanders had discovered an essential use for the animal’s dung.

Preserving meat by smoking it over sheep dung became standard fare. To protect livestock from harsh winters, farmers herded their flocks into barns. The animals spent the season eating, tromping on, and excreting hay. In spring, they returned to pasture-grazing and farmers were left to excavate the contents inside the barns. They dried the wads of hay and manure in the sun, then burned these pieces to smoke meats and fish in anticipation of the coming winter. Christmas, in particular, was a time for dung-smoked sheep meat.

Hangikjöt, traditional Icelandic smoked lamb, is still made over a fire fueled by excrement from the very same creature—perhaps not literally, but it’s possible. Cooks begin by dry-salting or brining a cut of leg or shoulder, then roasting the meat until it takes on an optimally savory, slightly ashen character. Locals continue to enjoy the meal as a Christmas dish, often served alongside potatoes, creamy sauce, and canned peas. It’s also a popular lunch food, usually in the form of thin slices set atop Icelandic rye or flat bread.