The secret of cooking, Wolfgang Puck confided in Ken Hom Travels with a Hot Wok (BBC2), is "a lot of prep and a lot of prep and a lot of prep". This roughly translates as having 35 underpaid sous-chefs who will stand for hours de-stemming bushels of coriander and chopping half a hundredweight of shallots into tiny dice. The master himself can then appear at the crucial moment, chuck the assembled ingredients into a hot pan and turn to the camera, saying, "You see, it's simplicity itself."

Puck, who is the chef-patron at Spago's, one of LA's power restaurants, also claimed in last night's programme that he loved nothing better than disappearing back into the kitchen at one in the morning to whip up a dish for a late arrival. This sounded distinctly unlikely, given that Hollywood is a notoriously early-to-bed town and that anyone less than Mike Ovitz or Steven Spielberg would be unlikely to send the owner bustling off to the kitchen, but never mind - such pledges of unspoiled culinary yearning are an important element in the PR pitch of any megastar chef.

Prep is important for telly cooks too, who would never be able to negotiate the hazards of demonstration if it wasn't for the fact that absolutely everything is to hand and perfectly measured out. And it's here that the discrepancy between what you see on the screen and what you replicate in your own kitchen is most likely to arise. As you delve into a cupboard for some vital ingredient, reaching past capers dating from the late Seventies, the scallops you have just put into the pan are inexorably transforming themselves from expensive luxuries into seafood-flavoured doorstoppers.

To be fair to Hom, the speed of his cookery is not just a concession to the expense of broadcast time - wok cookery is nine parts dull chopping to one part melodramatic sizzling and clanking, and the ratio is even more marked if, like Hong Kong restaurant cooks, you heat your pan with a decommissioned F-15 jet engine. Ever since Keith Floyd went alfresco, touring cookery programmes have shown an unreflective passion for the great outdoors. I suppose the calculation is straightforward; if you are paying all that money for the scenery then you had better have it in the picture. It's true that if your cook is going to be assaulted by ostriches or inadvertently set fire to the boat on which he's cooking - as happened in a recent Floyd series - there may be a point to such devices, but the convention is getting a little exhausted.

Last night, for example, Hom cooked up a Wolfgang Puck recipe on the roof of the Chateau Marmont Hotel. But the most interesting sections of the programme were not such postcard set-ups (who, by now, doesn't know what LA looks like?) - they were the moments when Hom went inside, to the Spago kitchens and to the home of a Hollywood scriptwriter - an open-plan dream of bread ovens, industrial gas burners and, through the picture window, a Hockneyesque dapple of swimming pool and acacia trees. Cooking is culture, not nature and it surely makes more sense to locate it where that culture is actually made. If the next series is to have an equally unwieldy title perhaps it could be something like "Ken Hom Pokes His Nose Round Famous Kitchens of the World".

A lot of prep has been done in Can't Cook, Won't Cook (BBC1), too - enough to make sure the programme flows, anyway, but not so much that disaster is entirely ruled out. The programme simply wouldn't work without its moments of incompetence, a cackhandedness which will ideally also offer the opportunity for some mild innuendo. "Mine's long and round, John. Yours is square!" Ainsley yelled yesterday morning, scrutinising an admittedly blocky attempt at a chicken roulade.

The essential seasonings for this dish - whichever celebrity chef is conducting the lesson - are a look of withering scorn, the conversion of cookery tips into a football chant, and a final twist of exasperated complicity with the audience. "What is he like?" said Ainsley, rolling his eyes at the camera as he applied the finishing garnish. Help yourself, I'm not hungry.