“That’s Kiki,” says the farmer, “… the object of my wife’s affection.” He picks up his truffadou (part animal prod, part digging tool) that rests with a leash on the trailer’s roof. Kiki responds with a happy grunt, or groin groin as the French call an oink oink.

It’s forty winters since Paul Pinsard found truffles – at least, started trying to find them. And it’s a pursuit that he will never tire of. Like another 2,000 hunters, or rabassiers, in this part of southwest France, he heads out on free days in the wintertime to gather truffles. Often he returns home with enough for a glamorous meal, sometimes a little more that he can sell for pin-money.

Monsieur Pinsard is a countryman – a paysan in this corner of Deepest France where the term ‘peasant’ isn’t belittling. A workaday farmer and elected local councillor, he is a rare breed: a rabassier that hunts with a truffle-hog.

It’s a tradition that harks back to Roman times, using a pig to sniff out truffles, and one that seems impractical in this new age, but there’s an end-of-season bonus. And it is revealed when he lowers the trailer’s tailboard and introduces ‘Kiki the Fortieth’.

Truffle-hogs are always called Kiki, and they’re treated like the family pet. Until April or May, that is, when the season is over and the little piggies end up crackling in farmhouse ovens.

Not that they are always ‘little’, or have such short-lived careers – sometimes old sows (that are as fruitful in the sty as in the truffle orchard) reach the size of Pinsard’s trailer, and can weigh in at a hefty 220kg. So it’s no wonder that dogs are the ‘nose’ of choice nowadays – after all, they can hop in the back seat of a Renault 2CV without crushing it.

The farmer’s wife was obliged to kiss and cuddle Kiki – and despite his tongue-in-cheek remonstrations, her husband would have encouraged it. A little bit of TLC goes a long way in the ‘breaking’ of a pig, especially when the collar and leash are first put to use.

Local trufficulture grandee Marthe Delon would have done the same. She was in her late teens when her mother-in-law handed her a truffle-hog as a wedding present and told her to cavage or dig up truffles. She retired in 2010 aged 82, but in her time she must have trained dozens of pigs – and some, according to local legend, lived the life of Riley. One, they say, made a habit of sitting in the parlour to watch the tv with her.

Kiki the Fortieth scents some ‘black gold’ at ten yards and scurries across to push its snout deep into the oak-leaf-carpeted soil. Pinsard drops dried sweetcorn kernels to distract the pig while he pulls out the ripe, golf-ball-sized truffle. “The baby truffe grows on the root of the tree in May,” the farmer explains, “After five weeks of feeding it cuts the cord and lives its own life.” From October the truffle matures; its colour changes from red to black; and its flavour and scent deepen – December’s light frosts intensify them even more.

Lot’s dry, occasionally chill winters are surprising for a département so southerly. Summertime’s hedgerows, meadow orchids and lush grasslands give way to flowering dogwood and bronze-leafed oak in December. And the river, after which the département’s named, gets a little choppy as it races along its tortuous course; a course punctuated by historic villages (some of France’s most beautiful) and ancient capital Cahors which sits in a vast, moat-like bow. Beyond, there's a realm of dense woods and rich farmland, vineyards and inland cliffs, and the limestone plateau known as the Causses, a protected ‘natural park’.

The Causses cover two-thirds of Lot and they are a deceptively harsh landscape. Groundwater flushes away quickly, down through the honeycombed limestone bedrock, so that the plateau’s thin coat of topsoil becomes a caked crust in wintertime.

Against this parchment-coloured backdrop, the truffières are easily spotted: orchards of young oaks – except these are upside-down orchards because the ‘fruit’ grows underground.

As we drive along country lanes lined with dry-stone walls, Fabienne Boussier – my guide when she’s not an acupuncturist in Cahors – chuckles at a memory. “When I was a girl in the 1960s everywhere seemed to stink of truffles in January. The Tuesday night train to Paris was piled high with wicker hampers stuffed with them. The smell was nauseating!”

That aroma! Like the knotty roots of an oak tree, the truffle’s aroma is a tangle of musky, nutty, earthy, with hints of cocoa, cognac and raspberry. It’s the kind of smell that wraps itself around you … It may be delicate, ephemeral, may last for just a few days, but when it is freshly unearthed it is so extraordinarily pervasive.

The truffle is the ‘spore-maker’ of an underground fungus – and for gastronomes the black variety must be tuber melanosporum, what Italians call ‘precious black’. The scent is simply a device to enable the fungus to propogate: like the “Eat Me” cake in Alice’s Wonderland, it entices animals to gobble the truffle up, so that the spores can be dispersed further afield.

On the road to little Bach, 13 miles southeast of Cahors, Fabienne points to telltale bare patches around some oaks. “They’re like witches circles,” says Fabienne, “where the truffles suck the energy out of the soil.” These patches are called brûlée – burnt – and are caused by the truffle emitting herbicidal compounds.

Monique Valette exploits the power of the truffle. She stores hers amongst farm-fresh eggs in the pantry so that the aroma enriches the albumen. Her Auberge Lou Bourdié is the restaurant to lunch at on a Tuesday. The likes of Cyril Lignac and Jamie Oliver – celebrity chefs from either side of the English Channel – have ended up in her cheerful kitchen, and pronounced her truffle omelet exemplary.

I catch her in the heat of service tending to half-a-dozen omelet pans like a circus plate-spinner. In between deft stirs and quick flips, she whisks more eggs and drops a finger-load of truffe brisure – broken pieces of truffle – into the mix. The finished omelets are then topped with slices of truffe brossée extra (the fine, brushed variety) that look like a row of buttons waiting to be undone to reveal the oozing insides. It’s what the French call baveuse – or ‘slobbery’ … which is how your mouth should be if it’s cooked right.

As well as the famed omelet, Monique uses other recipes that her grandmother perfected – including poularde demi-deuil, or ‘half-mourning chicken’, named after the bygone habit of a widow eventually moving from all-black to black-and-white attire. Here a young hen has a black-and-white appearance thanks to truffle slices slipped under its skin. The poaching liquor ends up as the base for Monique’s luscious mushroom soup that starts her 40 euro truffle omelet lunch.

Unlike the majority of Tuesday customers, Monique doesn’t go to Lalbenque truffle market, even though it’s just 6 miles down the road. Instead she buys her stash from villagers who turn up on her doorstep with just one or two pieces on offer. Those professional hunters that attend the market have spent the weekend digging up a bagful, and are looking for a price that Parisians or the Riviera crowd can afford – anything up to 1,200 euros a kilo.

From December to March each Tuesday, Lalbenque’s high street hosts its curious century-old spectacle: a 2pm-sharp face-off between fifty rabassiers and gangs of prospective buyers.

The truffle-hunters bring small wicker baskets containing their treasure; the prospectors their wallets bulging with notes. Both parties are separated by a long arm’s reach … but they’re close enough for questions to be posed. And though the rabassiers need only announce the weight of their supply, sometimes a buyer might be tantalised with a brief sniff.

Ding ding! And then at the 2.30pm bell, the cordon’s removed and they lock horns. Business is over within a haggle-filled, gesticulation-peppered half-an-hour.

Lalbenque’s market is the epicentre of the French truffle world. It’s a bourse that decides the price for the entire nation. And it’s an arena that tingles with small-time skullduggery. A rabassier unscrupulously plugs larvae holes with mud; a shady dealer hawks truffles out of his hatchback; gossipmongers whisper about a supplier bumping up stock with an inferior variety.

A while back one professionnel made the (not untrue) claim that his truffles were organic. “There was uproar!” exclaims Emmanuel Bréant of La Vayssade, an elegant boutique hotel in a converted manor on the edge of Lalbenque. In this part of the world, the quality of local produce goes unquestioned.

Nonetheless Emmanuel and his partner Hélène Baysse are careful not to take organic, free-range, hand-reared Lot fare for granted. They prepare delicious suppers for their guests using the very best: fennel and juniper, Quercy lamb, goat’s cheese, local foie gras and duck.

For Lot folk these are larder mainstays, not occasional treats – and in the season, the truffle is the staple of humble cafes as much as gourmand kitchens. After pottering around Cahors’ morning market, for example, try Auberge des Gabares for an effortless truffle omelet lunch (in the summer their wisteria-shaded terrace overlooking the river is a fine spot to enjoy ox tongue in caper sauce.) Or Le Ballandre – part of vintage Grand Hôtel Terminus, and one of the finest restaurants in the entire département – where chef Alexandre Marre devises tasting menus that are impressive, sometimes surprising explorations of the tuber’s versatility.

And on the road back to Lalbenque, at tucked-away Le Clos Caché, chef Mireille Combes takes simple, rustic repas and makes it elegant – think velvety broad bean soup bejewelled with truffle and foie gras.

To sample all of this cooking – let’s face it, luxury at piggy-bank prices – suggests Lot has the best of both worlds, but in reality its truffle industry is finding its feet again after a decade in the mire.

Jacques Pébeyre – whose Cahors family has been dealing in truffles since 1897 – blames the industry’s most recent challenges on the upheaval of the 1960s and 70s. “There are no paysans in the old sense. Fifty years ago many Lotois upped sticks and moved to the cities. Nowadays there aren’t enough people who care for the land – for the truffle grounds. Once, a paysan would be forever tending the truffières: watering and tilling; pruning; laying juniper branches to protect the truffles from a surprise frost. Nowadays, they don’t bother – it’s too much trouble.”

La Vayssade has its own truffle groves that will increasingly feature in the hotel’s ‘Truffle Weekends’. “The truffières are a long-term investment,” Bréant reminds me. “The oaks need replanting every 50 or 60 years … and for the first 10 they don’t produce. So, we have to wait a little – and hope, because only a third of spore-laden trees are successful.”

At the Chateau Haute-Serre winery, 4 miles away, they’ve started cultivating truffle grounds too. It’s part of the canny reinvention of a vineyard preparing for an uncertain future, a reinvention that started with its contemporary restaurant (occupying a converted chai or wine storehouse) that is increasingly well regarded.

As Jacques Pébeyre’s son Pierre-Jean told me: “When the wine-maker’s gloomy, the truffle hunter is smiling.” A good wine year (a sunny, cool, occasionally wet summer) is grim for truffles, and contrariwise. Perhaps the Chateau is planning a future where it’s a fruitful summer – whichever way the weather goes.

Now, in March, Lot’s rabassiers are gathering the last truffles of the season. They’ll soon hang up the leashes and little Kiki will be hunting for a hiding place. Over the summer months – as the Causses bloom, as holiday barges slip along the river, as the stalls of Cahors market creak under the abundance of seasonal produce, as wine is drunk on picnics in ancient woodlands – the truffles will start an extraordinary journey amongst the tangled roots of the oak. Somewhere. Perhaps.