True story. In 1974, a Parisian banker arrived home to find his cook had committed an act of treachery. She had served the very last truffle in his larder to her friends. He shot her. The judge, being a man of discernment, refused to try him, declaring it “a crime of passion, completely understandable and completely forgivable”.

As far as I’m concerned, it was the right verdict. Perhaps you have a passion for chocolate; perhaps you love your lobster. That’s fine. But truffles operate on an entirely different plane. The tuber melanosporum, the Périgord black truffle, is the most muskily orgasmic food on earth.

This winter has been a good one for the pungent black fungi, much better than last year — which makes a seasonal sally to the Lot Valley even more seductive than usual. If you can, drop everything and go in the next few weeks, while the little black beauties are at their peak.

When talking about truffles, it pays to be precise. There are more than 70 kinds in all, but only the white ones from Alba, in Italy, can hold a candle to the ineffable melanospora. And when foraging for such special titbits, it pays to have a helping hand. I was lucky to be in the company of two charming experts — Dany Chouet, a local chef, and her Australian partner, Trish Hobbs, the former patrons of the celebrated Blue Mountains restaurant Cleopatra.

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We started in Cahors, the medieval capital of the Lot département, mashed into a tight curve of the River Lot and overshadowed by grey limestone plateaus. This causse landscape is paradise for truffles. In the late 19th century, the Lot produced 20% of the total French crop of 1,000 tons a year. Today, the entire country manages just 40 tons.

For once, Dany explained, global warming isn’t to blame: the bountiful period a century ago was a by-product of the phylloxera that ravaged France’s vineyards. Farmers, seeking alternative crops, planted oaks in known truffle zones, and the results exceeded their dreams. Delicacies once reserved for royalty became so common, country folk used to eat them whole.

That golden age ended with another catastrophe, the first world war. The subsequent lack of manpower coincided with the end of the 30-year productive life of the truffle fields. Suddenly, truffles were scarce. They have been ever since.

In Cahors, Dany and Trish took me to visit their friends the Peyberes, France’s leading truffle merchants. “We can never get enough to meet demand,” Babé Peybere told us as we roamed the family’s sublimely fragrant factory, where workers brush, sort, jar and ship some of the crop.

By the end of the tour I was a drooling wreck, but lunch was coming to the rescue. The Balandre restaurant, in Cahors, serves a menu marché de truffes on winter Tuesdays, with truffles in every course. Meals don’t come more memorable than this. A large truffle shaving curled over my foie-gras-laden chestnut velouté; truffled lentils wreathed the paupiettes de veau; the Coulommiers cheese was sandwiched with truffles, the panna cotta studded with truffle bits.

The main course, however, was still to come — a trip to the Tuesday truffle market in the village of Lalbenque.

Everyone was there, from grizzled caveurs (truffle-hunters) in battered berets to chatelaines in Hermès scarves. A rope separated us from the vendors and their troves, arranged in cute Red Riding Hood baskets on long tables.

And oh . . . the smell. The aroma of hundreds of fresh, perfectly ripe truffles came at us in waves, a shocking wall of wild, pungent perfume, the Chanel No 5 of the earth.

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