Under a spreading chestnut tree...

For centuries, chestnuts have been the lifeblood of Corsica, providing food, wood and even currency. And every Christmas Eve, their sublime sweetness celebrates another rich harvest

In the Tasso family kitchen in the village of Tasso, Anthony is singing "The Chestnut's Lament". Hand clasped to his ear in the posture of polyphony – the ancient Corsican art of unaccompanied song – the sound is as unearthly as a throat can produce. "For generations I've fed you, given fodder for pigs, wood for furniture and fuel, but now you forget me, let the maquis strangle me."

The 40 Tasso dwellers are not the accused. Their village still nurtures the old symbiosis, sustained by its trees for 500 years. The Tasso family has been here as long – Anthony the latest in a lineage of millers.

Anthony's mill smells of autumn bonfires. He dries the nuts over chestnut-wood embers, grinds them to flour on stones that his ancestors dragged from the river. Hams of chestnut-fed pigs hang curing in the smoke. It seems like just another cottage industry, yet villages like Tasso are guarding Corsica's Holy Grail – the chestnuts they produce the essence of every Corsican's dream.

Chestnuts were for centuries the island's staple food. The love they still inspire, evoking mum's cooking and grandparents' stories, renders Corsicans lyrical. The Tasso villagers, prosaic mountain people, spoke without embarrassment of the statuesque majesty of the ever-giving trees.

The chestnut's conquest of Corsica dates from the 15th century. Following centuries of upheaval, fought over variously by Saracens and Pisans, Spaniards and French, the Genoese Republic imposed some control. The island soars from the sea to untamable mountains with little space for agriculture. Faced with frequent famines, its far-sighted governor forced landowners to plant four trees a year – a cherry, a mulberry, an olive and a chestnut. Generous and undemanding, within a few decades chestnuts reigned supreme. Soon known as The Bread Tree (12 fed a family for a year) the nuts were used as currency, turning the island into a chestnut economy. Wedding feasts comprised 22 different dishes of the arboreal gold.

The most prosperous region was Castagniccia – literally Chestnutland. Long untended, the once functional forests are now a lovely sylvan wilderness where we picnic in a glade of shady centenarians. Many villages are derelict, but the baroque towers of their chestnut-wealth churches still rise above the trees. The black pigs we meet along its sinuous lanes look smugly plump on their abundant windfall booty.

The chestnut's gift of self-sufficiency fuelled national aspirations that with occasional eruptions – including a brief comic-opera monarchy – have simmered ever since. (During our trip, 20 French-owned buildings were bombed.) Pascal Paoli, a Castagniccia-born Anglophile rebel who from 1755 to 1799 led a utopian democratic republic, said, "As long as we have chestnuts, we shall have bread".

Attacked by France, he allied with England. His homeland became an Anglo/Corsican kingdom imperiously ruled by George III's viceroy. Pascal was banished, far from his trees, and died in London. Napoleon's statue in Ajaccio may be bigger, but from Pascal Paoli's, revered as Father of the Nation, permanently flutters in his old capital of Corte the island's Moor's Head flag.

In 1796 the French came to stay, professing consternation at the chestnut monoculture – 70 per cent of all cultivable land. The tree was deemed "immoral", its toil-free income promoting sloth and fecklessness. But facing suppression, the bountiful nut proved tough to crack.

It took the First World War – from which one in five of the men failed to return – to do the Bread Tree down. In depopulated villages crops went ungarnered, wheat was imported, chestnuts devalued to poor man's food. During the Second World War, German and Italian troops picked the island clean. As Corsicans joined the Maquis resistance, the spiky manna averted starvation – yet it seemed the nut's last stand. Years of surviving on chestnuts left a generation whose stomachs yearned for novelty.

The faithful fruit was shunned. Villages such as Tasso looked destined for school history books. But they were saved by distant patriotic palates. Every Christmas, grannies sent flour to homesick emigrants who longed for the chestnut taste of Corsica.

And today, with what seems part inherited nostalgia, part gustatory statement of their distinctness from the "continent" – meaning mainland France – Corsicans again are tucking in to their culinary legacy. The prosaic ancestral staple has been elevated into rustic haute cuisine. Asked their favourite dish, expressions grew dreamy. Chestnut flour pulenda – polenta – served with brocciu, the island's ubiquitous ewe's milk cheese, topped with figatellu, a kind of liver faggot, or crisp pancetta and fried egg.

The Tassos of Tasso cannot meet demand. Tourist boutiques sell gourmet patés, biscuits and aperitifs – occasionally, if you're lucky, ribbon-tied bags of smoke-flavoured flour. At the Bocagnano Chestnut Festival, an epicurean party the first weekend in December, ever-growing crowds reflect the nut's renaissance.

They are celebrating too their music and language, the rich island life few tourists see.

With its sparse population, few motorable roads, the interior resembles a chunky slice of Eden. You understand why Corsicans love their chestnut trees. Softening the serrations of their angular island, merging with forests of 1,000-year-old pines, they make it the greenest in the Mediterranean. We leave the perched village of Ota to climb the spectacular Spelunca Gorge. The chestnut-shaded lane is hemmed for a kilometre by enormous family tombs like posthumous vows of the occupants' adhesion to their shallow native soil. In the Porto river valley, the track soars over three slender Genoese bridges. The Spelunca Gorge – eagles hovering above the vertiginous walls – with white-water rapids, flower-filled forest, dip-inviting pools, seems a microcosm of Corsica's delights.

We arrive in Evisa – another famous chestnut village – hungry and thirsty, to discover La Châtaigneraie, François Forascieppi's small hotel-restaurant set in a chestnut grove. François' childhood village chestnuts lured him home from years abroad, with Marcy, his Californian wife. Marcy had never tasted a chestnut but now reels off her menu with starry-eyed passion. From hors-d'oeuvres to desserts – some traditional, some François' creations – everything is chestnuts. All are from the hotel grove – smoked and ground in the village mill. In such sensational walking country, they get many tourists. But these days, compatriots are their hungriest fans, travelling miles for blowouts from great-grandma's cookbook.

Nibbling home-cured saucisson, a memory returns of the Tassos of Tasso – Anthony singing in spine-tingling bass Dio Vi Salvi Regina – God Save The Queen – the Corsican anthem. The other villagers, some with moist eyes, join in, voices filling the island's silent heart. They had entertained a stranger, but this was for themselves.

Like the Moor's Head, chestnuts may seem a strange national emblem, but, as you recall the few proud sovereign years, it's easy to see how they can be viewed as living monuments to a self-sufficient age. They are the leafy daydreams of autonomy that few believe is viable and symbolise that independence of identity met at every hairpin turn.

Marcy serves us chestnut-fed ham, wine-braised boar with chestnuts and chestnut-flour flan topped with chestnut cream. We could drink Pietra – a chestnut-based beer now the island's top brand – but it seems a bit de trop. The meal surely deserves good Corsican red wine? Still, François insists we try his chestnut liqueur as digestif.

Ray Kershaw reports from Corsica for 'The Food Programme' on BBC Radio 4, at 12.30pm tomorrow, repeated at 4pm on 23 December

A treat for sweet-toothed gourmets

Marrons glaces: the connoisseur's chestnut

Tiny Collobrières, hidden in the forests of the Massif des Maures in Provence, is internationally revered by sweet-toothed gourmets. Its fabled marrons glacés, bigger than golf balls, mellifluous as honey, are to ordinary chestnuts what foie gras is to faggots – the caviar of confections.

Its chestnut trees were planted in the 12th century by the still-surviving monastery of La Chartreuse de la Verne. One gnarled specimen is 1,000 years old.

While the majority of chestnuts hold several small kernels, a marron contains one giant nut. Both types grow on the same tree, but generations of selection have bred the aristocratic Marron de Var, the Collobriérois variety that yields the highest ratio of chubby-cheeked marrons. Even so, only a quarter achieve the glamourous career path. At thirty marrons to the kilo, they fetch four times more than their plebeian kin.

In October the ripe nuts open and fall. The Ferrara family – one of the 100 growers – invites friends to collect them, a jolly occasion, aching backs anaesthetised by the local rosé wine. The Confiserie Azuréenne – permanent workforce seven – suddenly buzzes with seasonal staff transmuting the harvest into edible gold.

Marrons glacés, 17th-century favourites at Louis XIV's court, are thought to have been invented by the Sun King's own confectioner. Their succulent texture has since kept them synonymous with extravagant indulgence.

The alchemy takes time. After baking bursts the shell, each nut is muslin-wrapped, and for 72 hours it's left simmering in syrup, doubling its size and weight. Conserved in syrup, they keep for five years, the flavour improving like a fine wine.

Their final metamorphosis awaits customer orders. Once completed, eat-by deadline is three weeks. Coated with a secret recipe glaze, they are delicately dried. Many are damaged – only the perfect make it to the packing room. Hand wrapped in gold foil, in embossed wooden boxes, occasionally silk-lined, they are sent around the globe. The largest box of 42 costs £45 – £30 buys a kilo of broken bits.

Christmas is traditionally marrons glacés high season. Should Père Noël next week be particularly munificent, locals recommend them with a dry red wine to accentuate their sweetness.

Traveller's guide

Getting there: There are not yet any direct scheduled flights from the UK to Corsica. The easiest approach is on a cheap flight to Nice (eg on British Airways, Bmibaby or easyJet) and transfer to a domestic flight for the short hop to Ajaccio. Or you could take a ferry from Nice.

More information: French Travel Centre, 178 Piccadilly, London W1V 0AL (09068 244 123, www.franceguide.com).