The French Laundry at Harrods, Fourth Floor, 87-135 Brompton Road, London SW1

Wow! Brilliant! Insane! Our reviewer is blown away by Thomas Keller's London pop-up

This is not a restaurant review. I didn't pay for my dinner and you won't be able to eat at this establishment. So this breaks all the rules – which means you can take the mark out of 10, below, with a pinch of salt. But the 10-day pop-up version of The French Laundry (open till tomorrow) should not go unmentioned because it is, quite simply, extraordinary.

Regular readers will know from John Walsh's masterful interview in the 25 September issue with Thomas Keller, chef/patron of the three-Michelin-starred Californian institution, that his temporary home in Harrods is not an overture to opening a London outpost. Rather, this is the maestro allowing us Brits the chance to experience his food without jetting over to America, by jetting himself, 30 staff, plenty of tableware and inordinate amounts of butter to the UK.

The wisdom of this decision must be judged by what is on the plate. It must surely have been Harrods' decision to create an anteroom to the restaurant with astroturf and fake lavender plants on garden furniture. It puts one less in mind of the Napa Valley than B&Q. A facsimile of the original's blue door swings open for the big reveal, but instead of a light-flooded, luxuriously appointed room, the temporary French Laundry is more of a generic conference centre. For £250 a head (without wine), I want to be bathed in atmosphere, not noticing a blown lightbulb, and a clump of exposed plug sockets and extension cables.

Perhaps I'm being a grinch. There's an army of charming staff who anticipate each diner's every need, and perform the intricate task of delivering, describing and revealing each dish with aplomb. On fine white napery, bone china and dinky cutlery is placed down and whisked away in choreographed moves that put Strictly to shame. And there's a 26-page booklet about the purveyors of the produce.

So, that food. A pre-starter of a tiny Gruyère choux bun and smoked-salmon and cream-cheese cone ("a Jewish Cornetto", my friend Angie quips) slips down like the devil in velvet trousers.

The first dish of the nine-course tasting menu proper, a signature French Laundry dish called "Oysters and Pearls", ditto. I might never have ordered a sabayon of pearl tapioca with oysters and caviar; it sounds at once salty and slimy. But in the hands of Chef Keller, it is laugh-out-loud joyous – smooth, tangy, plump oysters and unctuous creamy sabayon offset by bursts of rich caviar. It is, for me, the high point of the meal and a shame that it comes right at the start.

Next, a salad of hearts of palm that has the tiniest radish garnish I've ever seen; these and the candied pili nuts (pronounced peely) have the unfortunate effect of setting off a fit of the giggles around my table, and our convivial mood seems a little at odds with the reverential quiet around us. We feel like naughty children – or the bad mice of the Beatrix Potter story, given the doll's house size of the dishes and cutlery.

The menu would take the entire page to list fully – there's a truly dazzling array of components and techniques on display (a full menu will be displayed on The Independent's website). We even spend some time discussing the brilliant insanity of "potato glass". If I wish for anything, it's for there to be the occasional course without an essence or foam to allow my palate to relax.

I eat more brioche than on a weekend in Paris. Beef, foie gras, lobster, ibérico ham, caviar and chicken at one sitting is a bit "oof". I find myself thinking, this is overwhelming, but I must enjoy it, I'll only do it once. Then come puddings. Huckleberry sorbet is zingy and quite, quite beautiful. An unadvertised extra – coffee and doughnuts, pictured – is a delectable cappuccino semifreddo and cloud-light cinnamony buns.

Then, just before Keller comes out to see how we got on, a china flying saucer is brought out – it contains his five favourite "movie snacks". But if you ever find crisps, mint creams, Raisinets, root beer or cola cubes like these at the multiplex, you've died and gone to heaven.

Feeling rather like a poisoned pup, I sit back listlessly until my husband invites Keller, the Thomas Keller, round to our house for shepherd's pie. He figures that even the world's greatest chef needs comfort food sometimes. Pressure! Mercifully, he's a tad too busy wowing London's richest foodies with his supercharged mega-menu to accept.

8/10

Scores: 1-3 stay home and cook 4 needs help 5 does the job 6 flashes of promise 7 good 8 special, can't wait to go to california 9-10 as good as it gets

The French Laundry at Harrods Fourth Floor, 87-135 Brompton Road, London SW1. Open till tomorrow

Talking shop

Café 21, Fenwick

First Floor, French Salon, Northumberland Street, Newcastle upon Tyne, tel: 0191 260 3373

Be prepared to queue for this in-store spin-off from the city's famous Café 21. Quality salads and snacks; popular for brunch

First Floor Café, Lakeland

Alexandra Buildings, Windermere, Cumbria, tel: 01539 447 116

The dining-room – presided over by a chef once of Le Gavroche – offers excellent fresh food and quick service

The Fountain, Fortnum & Mason

181 Piccadilly, London W1, tel: 020 7734 8040

Incredibly under-rated as a breakfast destination, the genteel buttery is also worth seeking out for its scrumptious afternoon tea

Reviews extracted from 'Harden's London and UK Restaurant Guides 2011' www.hardens.com