My mother had a friend with a restaurant on a French beach. For two weeks one summer, we lounged around browning ourselves in the vain hope that we could transform ourselves into Bardot lookalikes. At lunch, we sat beneath woven bamboo canopies, feet in the sand, gnawing barbecued corn on the cob. Recalling that blissful scene summons the toffee-ish taste of charred corn. We discovered that the chef bought whole cobs in cans, because they barbecue better than fresh. Like holiday wines, however, the canned sweetcorn we got at home left no such butter-kissed impression. Watery, salty and somehow an invasive, ugly yellow when added to any dish, I doubt canned sweetcorn will ever become a fashionable food. But another type of corn has. The potato crisps on every snack-bar counter have been re