But the legend about this distinguished prune has not extended to Britain, where in uninformed isolation, these exceptional fruits turn up for sale saying simply 'Prunes' and in small letters 'Produce of France'. Why?
Those who source our dried fruit, it seems, believe the British public might be confused by information about pedigree and provenance. Prunes should be small, hard and miserable - an unremarkable commodity. 'They are scared to promote something new,' says a spokesman for one of the largest exporters of pruneaux d'Agen, Maitre Prunille. 'They' are also saddled with the memory of their first prunes, served with 'custard' in the school canteen, which have given many British their 'never again' image of the fruit.
Inhabitants of the Lot and Garonne in France have been drying a particularly delicious variety of purple plum - le prunier d'Ente - since the 12th century. They are a world apart from the mean little school dinner specimens (often a second-grade cash crop from Eastern Europe).
The modern Agen prune is large, moist and delicious - good enough to snack on without any soaking, luscious in compotes, dark and moist in cakes. Its uses can be savoury as well as sweet, doing wonders, among other things, for a coq au vin. The best pruneaux d'Agen you will ever taste are the new season's 'mi-cuit' or half-dried ones, which appear in markets throughout the south-west in the autumn. These shiny, wrinkled pruneaux are nectar and, unlike most prunes, they actually taste like the plums they come from.
Visiting the orchards at harvest time is an experience. Rows of trees, heavy with fruit, stand surrounded by circular blue carpets of fallen plums, because the plums must only be harvested when the fruit is dropping from the tree. Unlike the purple, black and fuchsia golf balls which come from countries such as Chile and South Africa throughout the winter months, these plums are a dream. They are the best I have ever tasted: even better than the finest Victoria or Quetsch. Shaped like tiny rugby balls, the plums feel too firm to be ripe. But taste them, and they are almost sugary sweet and running with juice.
Despite producing a formidable 32,000 tonnes of pruneaux a year, the Agen prune business (unlike California's) remains formidably artisan. There are 3,400 producers, many of whom are quite small. The drying of the plums is often carried out by the producer, though there are several large communal drying stations. Much of the picking is still done by hand, as is the quality control and the grading for size.
The key to drying plums is the end humidity, or moisture content. For consumers looking to buy good pruneaux, seek out those with the highest possible humidity: these are the largest, softest-looking prunes. Throughout Europe, you can buy prunes with up to 45 per cent humidity (almost mi-cuit), though 35 per cent is more common.
In Britain, though, unfounded fears about preservation and the search for an infinite shelf-life mean that maximum humidity is kept to 29 per cent, thus ensuring a harder, less succulent product. But even at this degree of dryness, you will be able to distinguish Agen prunes from plainer imports, dried to a safe (and dull) 23 per cent.
How cheering it would be to see those bright and appetising Agen prunes shining out from the shelves in squashy, sweet-smelling packets. Might not lateral thinking, too, elevate a fine product such as pruneaux d'Agen from the neighbouring dreariness of dried dates to the fruit department where they belong?
And while we are at it, if we can have fresh Medjool dates from California, why not some gorgeous mi-cuit pruneaux d'Agen in season? I rest my case.