Smen is salted, fermented butter that ages like fine wine. The longer it sits, the more of a delicacy it becomes. And with proper care, smen can sit for a very, very long time.

Legend has it that Berber tribesmen would bury a clay jar of smen on the day of their daughter’s birth. Only on her wedding day would they unearth the jar for use. The notion isn’t far-fetched: Clarifying, salting, and fermenting smen, as well as keeping it cool, gives the butter a lengthy shelf life.

The longevity of this Moroccan delicacy relies on the formation of lactic acid, which prevents spoilage and imparts a blue cheese–like scent. After churning cow, sheep, or goat milk into butter, smen-makers clarify the liquid by heating it and straining out the solids. They will jar, salt, and sometimes herb the butter (usually with a combination of oregano, thyme, rosemary, and fenugreek), then leave it to age in a cool, dark place. As the smen sours, good bacteria flourish, adding to the pungent flavor profile. These musky microbes also stop harmful bacteria from forming. Keeping smen cool in a pantry or underground also helps preserve the rich butter, especially during Moroccan summers.

In Fez, families with generations of smen-making wisdom gather in one well-known square, called Qaat Smen—the epicenter for superior fermented butters. Vendors sell their unique versions for cooking cous cous and tagine, for spreading on bread, or even for stirring into coffee. This funky ingredient regularly appears in Moroccan recipes, but is far less accessible outside the region. Just bury some salted, clarified butter in your backyard now; it’ll be ripe and ready for next year’s Moroccan feast.