In late February it was snowing in the Luberon mountains of Provence. Long, parallel rows of lavender in the fields were just discernible through the fresh powder snow. I was there, high in the mountains near Apt, in the company of two Tasmanians with a passion, a mission in life - to grow the Perigord truffle.

The botanical name for this truffle is tuber melanosporum, and it is an unprepossessing beast; black, warty and subterranean. But for gourmets the world over it is spoken of with hushed reverence, for this little fungal tuber can cost upwards of £400 a kilo. Its flavour and pungent aroma are a gastronomic delight. In the mushroom world this truffle is king, although it pays allegiance to the famed white truffle of Alba, the tuber magnatum.

What makes this perfumed fungus so special is not just its value - the Alba truffle can fetch five times its price - it's the fact that now it can be grown commercially. And that's why I was in the company of Duncan Garvey and Peter Cooper who were taking me to meet one of Provence's commercial truffle growers, Bernard Marrenon. Peter and Duncan own the 'Perigord Truffles of Tasmania Company' and once a year they come to France during the season to exchange information and technical know-how with the French growers.

Finding information on truffles other than old wives' tales is not easy. Furtiveness and secrecy are the hallmarks of the trade. Those who collect the wild truffles guard the secret of their whereabouts jealously - no one will show you how to train a dog to find them, no one is sure precisely what conditions are needed for their growth, or why they should grow beneath one tree but not another. People lie. The reason for this secrecy is simple: there's a lot of money to be made with black diamonds.

Duncan and Peter have been chasing their dream for a long time. Extracting the information they needed was slow, but they did have something going for them. The normally secretive French growers were eventually prepared to talk to them simply because they were Australian. They could never be in competition because their Australian season is six months later than the French. If they ever exported to France it would be when no one else had any to sell. It was safe to talk to them.

February is high truffle season; from the Perigord to Provence the truffle markets are in full swing. These are not elaborate affairs: the closest equivalent we have to them are car-boot sales. Men stand shiftily around with the boot open, perhaps a canvas bag just visible with the precious contents hidden from view. Like any other mysterious operation there are traps and pit-falls for the unwary. Other truffles like the Brumale look like the Perigord, and if stored in close proximity can start to smell like them as well. Or a novice could easily find himself in possession of the summer truffle - the tuber aestivum - a far inferior fungus that sells for a tenth of the price of the Perigord: or at least it should. And now, increasingly, there is the Chinese truffle. Imported from China where it can be bought amazingly cheaply, it can often be found in the hands of unscrupulous traders masquerading as the real thing. It looks like it, it smells like it, but its flavour and aroma are pale shadows of the melanosporum.

Into this traditional world of clandestine activity and arcane knowledge has stepped the French government. Various agencies have got involved: the Ministry of Agriculture, the National Institute of Agricultural Research and the Technical Centre for Fruit and Vegetables. Government scientists are slowly unlocking the truffle's secrets. It makes sense to do so. Truffles grow on wild, abandoned hill-sides in symbiosis with trees. So land that would produce at best poor timber that would be hard to extract, instead produces a crop that is easy to transport and is extremely valuable even in tiny quantities. For a rural Provence that has become increasingly depopulated, it represents a very real prospect of prosperity. All you need are the specially prepared saplings and somewhere to plant them and you're ready to become a truffle grower.

So is this the goose that lays golden eggs? Well yes and no. Firstly the government approved inoculated trees aren't cheap and there are no guarantees that you'll ever find a truffle beneath one. Secondly you have to wait ten years before your first flush of truffles should there be any at all, and thirdly you have to contend with predation. With this kind of wealth lying just beneath the surface it should come as no surprise to learn that some people come around at night and steal them. Survive all this, then you have to find the underground truffles. You can't just plough them up like potatoes or you'll have none next year. You have to lift them carefully one at a time, and to do that you need a trained dog to show you where to look. Which leads to this circularity: to train a dog you need truffles, but until the dog's found some you don't have any.

So there we were in a snow-storm while Bernard led us to his trufferie. He planted it twenty years ago, so it's now in full production. The trees are planted in lines, about six metres apart. We walked slowly along watching Minouche, Bernard's dog, who occasionally stopped and started to dig. The ever-vigilant Bernard would step in, push Minouche aside, and gently lift his black treasure from the ground. He used a bigot, the traditional long-handled two-pronged fork to do this: it gently breaks up the ground enough to remove the truffle, but not so much as to kill further production. After forty minutes or so we had about a kilo of truffles when the blizzard forced us indoors for coffee and marc. It was a brief taste of Bernard's way of life. For three months of the year he works his dog in the trufferie twice a day - late morning and early afternoon. He has three dogs which he alternates day by day because their little paws get sore from all that digging and they need time off. The rest of the year it's maintenance; pruning, keeping down weeds and planting new trufferies.

This was a real treat for me; I've long had a fascination with truffles, and getting into the inner sanctum of the grower fraternity was a privilege, and was staggeringly informative. I learnt more from the growers in those few days than I ever did from books. But now, just as I'm about to write down some of the best kept secrets of the truffle, I've noticed that I'm out of space.