Digging into the varied and distinct regional cuisine is a tempting impetus for visiting to Mexico, but the signature dish of the country's culinary capital, Oaxaca, is the rich, dark, mysterious mole negro (pronounced MOH-lay). A traditional sauce that is typically served with meats, mole negro captures the complexity, fanatical tradition and inimitable traditions of the country itself.

The intoxicating taste is among the world's great secret sauces, with a thirty-odd ingredient blend including unsweetened chocolate, roasted nuts and chillies, onions, garlic and cure-all medicinal leaves of yerba santa (sacred herb). The time- and effort-intensive dish, which is traditionally served at Oaxaca's plentiful religious festivals, remains a sacred experience for the taste buds.

Oaxaca: The heart of Mexican cuisine
To get to the source of the sauce, begin in Oaxaca City, the elegant seat of the southern Mexican state by the same name. Like the dish you are after, Oaxaca City is a treasure born of the long and varied traditions which have come down from the surrounding Sierra Madre mountains. There, ancient Zapotec and colonial Spanish influences make a colourful intoxication of the senses, a scene set by musicians strolling along the shady plazas playing indigenous melodies, colonial facades lining the narrow cobblestone streets and the region's famous mole sauces. Oaxaca has a seven-colour rainbow of mole varieties (including mole colorado, which is dumbed down and exported as enchilada sauce). Each has its own seasonal and traditional place on the menu - but the black is the most complex, the most difficult to make, the most exciting, and it should be among the traveller's first tastes of Mexico.

Oaxaca City's zócalo, or main square, is the place where lovers snuggle on park benches and visitors enjoy long, leisurely lunches at outdoor cafés. Each one of these touts their own mole negro; choose carefully, most locals head to the cafés south of the plaza where the recipes served in hole-in-the-wall lunch restaurants are closely guarded family secrets. Here, a typical set lunch will consist of three servings - a bowl of brothy soup, a mole dish consisting of a meat dish smothered in smoky, mildly spicy sauce and eaten with fresh, made-to-order tortillas, and a simple dessert of fresh fruit.

Making magic mole
Think you are ready to recreate the magic yourself? Good luck, chef. Making mole negro is a process that, like so much regional Mexican fare, is an arduous labour of love that can be daunting for the first timer. The process to make a batch of mole negro involves roasting pumpkin seeds, nuts and chillies and sourcing ingredients that most of you may have a hard time finding at the supermarket back home. If you are quick, it can take most of a day. Even so, all is not lost for those with a tight agenda; Oaxaca has a clutch of excellent cooking programs, some of which are associated with renowned restaurants and language schools. This can help cut a few corners, just in case an 8-hour seed-roasting session is not a dream holiday. In a typical Oaxacan cooking program students are guided through local markets in the morning and sit down to a tasty and satisfying homemade lunch. If this is still too much effort, vegetable markets in the city sell mole paste which can be reconstituted at home.

Sampling Oaxaca's best
The question of which restaurant turns out the best mole negro in Oaxaca is something that has been fodder for debate for generations, but for a sure bet visitors should leave Oaxaca City centre and visit the nearby village of Teotitlan de Valle, a town renowned for producing hand-woven and naturally dyed textiles. Chef Abigail Mendoza Ruiz's lunch-only fine dining restaurant, Tlamanalli, turns out the finest traditional Zapotec recipes - which include several moles, depending on the season. Accompanied by a splash of locally produced mescal, the simple dining room offers moles negro which are sophisticated, smoky and seem to evoke the earthiness of the ancient hills of Oaxaca. When you ask Ruiz if she'd offer her own mole negro recipe, she shrugs her shoulders. "Sorry", she says. "An old secret."

The article 'Mexico's ultimate secret sauce' was published in partnership with www.lonelyplanet.com.