U.P. at Dominique Ansel Kitchen, 137 Seventh Avenue South, New York (dominique anselkitchen.com). Tasting menu for two with drinks, $270

A friend of mine, a big wheel in the food side of the high-street coffee-shop business, has a simple theory about the products she sells. “People generally only buy cake for one of two reasons,” she told me. “Because they’re happy and because they’re sad. It’s an entirely emotional purchase.” I suspect the vast majority of people who have bought Dominique Ansel’s products in New York have done so because they were happy. You’d have to be, to justify standing in line for the 45 minutes required to purchase one of them.

French-born Ansel was Daniel Boulud’s pastry chef in New York for many years before setting up his own business and creating the Cronut, a hybrid of a croissant and a donut. Perhaps you’ve heard of it. Perhaps you imagine it’s hyped. It really isn’t. I won’t queue for anything, but I did queue for a Cronut and I didn’t begrudge a moment of it. The flaky, laminated croissant-style pastry is deep-fried, dusted with sugar and then back-filled with flavoured cream. It’s every kind of good. I was grateful for the two-per-person limit. Without it I would have ended up face down in a tray of them.

And he’s not just a one-trick pony. There’s the DKA, his take on a Breton pastry, which is a caramelised croissant, with a soft flaky interior. There’s the frozen S’more, an ice-cream block wrapped in chocolate, then enrobed in marshmallow and frozen. There’s his soufflé inside a brioche shell and his shot glass fashioned from chocolate chip cookies. You get the point. Ansel is the king of happy.

So when I heard about U.P., short for Unlimited Possibilities, his dessert-only tasting-menu supper club in New York, I had to go. Seven courses from the inventor of the Cronut? Get me a stunt pancreas and hail me a cab. I pulled strings to secure a booking for when I would be in the city, because there are only eight places at the limited number of sittings, and each tranche of 800 seats sells out in minutes. I happily coughed up the $135, reasoning that the stupid price only added to the excitement (plus this included a cocktail pairing; without drinks it would be $85.)

I didn’t even baulk when the youthful waiter greeted us at Dominique Ansel Kitchen, his shop and production base at the bottom of 7th Ave, with the news that the team upstairs was “super-excited” to meet us. The only adult who should ever be described as “super-excited” is the middle-aged chap who has overdosed on Viagra. But hey, I was here for killer dessert, not sincerity.

What followed was one of the most disappointing of culinary experiences. It was proof, if proof were needed, that where food is concerned deliciousness is always more important than theatre, and that the gifted should recognise their limitations. Through seven courses of dismal, overconceptualised, crushing mediocrity, Ansel proved himself so far out of his depth it was a wonder he could still breathe.

We were led upstairs to the production space, lit by a buzzing strip light. With sombre ceremony a table was lowered from the ceiling, and legs screwed in place. If these people were super-excited to see us, they were very politely not showing it. Alarm bells rang when we were told our meal’s theme was to be the American Dream. It started badly with a savoury course – a beetroot cracker with a scoop of spiced yogurt, which I ate obligingly. I mean, really! I didn’t come here for this. Bring on the sugar.

For the first course, celebrating the gold rush, we were each given a miniature version of the sieves used to pan for gold, filled with coffee grinds. We were to shake it to reveal two nuggets, one containing acacia honey ice-cream, the other a bread and butter pudding made with sourdough. These set the scene for the night: without having been told what they were we wouldn’t have known. They were just misshapen balls of sweet cold stuff. The sieve gimmick was overly cute, the dish it served a complete letdown.

Carpe Diem, celebrating the jazz age, began with a fake champagne fountain and finished with a bowl of exceptionally lacklustre summer pudding made with brioche. M&S make a better summer pudding. The 1950s dream of home ownership was celebrated by the arrival on the table of pop-up paper cut-outs of houses with white picket fences. The food element was something instantly forgettable involving curls of persimmon and an unidentifiable root dotted with strawberry and cherry tomato purée.

The age of peace and love brought the most edible dish, a rather lovely panna cotta, all silk and set dairy fats, flavoured with camomile. But it was back downhill from there. Wall Street was celebrated courtesy of a “cigar” made with a slightly soggy potato tuile, filled with an overly subtle chocolate ganache and cream, presented inside a glass dome filled with smoke. It was clumsy symbolism, followed by an extremely disappointing bit of pastry work. The drink with this summed up the dreadful cocktail pairings: a huge, fruity Cabernet Sauvignon completely ruined by the addition of a peaty whisky. It’s the sort of drink kids invent when pissed at the end of a teenage party by decanting other people’s leftovers into one cup.

The tech age involved a fake old-style Apple Mac, into which we shoved a floppy disc. In return it spat out a waffle, to be topped with tonka bean ice-cream. A waffle as made by Ansel should be the best waffle you’ve ever tasted, a celebration of crunch and soft and hot sweet air. It should be the kind of waffle you would queue for. This one arrived without me even having to stand up let alone queue, and I still felt short-changed. It was dark, crumbly and slightly bitter as, by this time, was I.

Look, I don’t think less of Ansel’s patisserie products because of this. He’s due to open an outpost of his bakery in London later this year and I urge you to try his Cronut, it’s brilliant. But I do think less of him for believing $135 for this victory of style over substance, for this pompous, self-important exercise in paper cut-outs and props, is in some way OK. Because it really isn’t. It made me sad.

Jay’s news bites

■ London now has its own dessert restaurant at the Café Royal. It’s headed up by Sarah Barber, former head pastry chef at Dinner by Heston Blumenthal. The menus run from £26 for three courses to £42 for five and include her take on the Jaffa Cake, a dish called ‘Eat Me, Drink Me’ involving both a version of a Snickers bar and a malted chocolate milk shake (hotelcafe royal.com).

■ The Manchester branch of Hawksmoor is to get competition. The team behind the small Solita Bar and Grill chain, known for its burgers, is to open the Solita Steakhouse in Barton Arcade on Deansgate. Co-owner Franco Sotgiu says it will be a ‘grown-up version’ of their other restaurants (solita.co.uk).

■ Phil Howard, head chef of the highly regarded Square in Mayfair’s Bruton Street for 25 years, has stepped down following the restaurant’s sale to the Marlon Abela group. Abela praised the restaurant’s ‘modern fine dining’, though what he’s buying is an interesting question given all of that was led by Howard (squarerestaurant.com).

Email Jay at jay.rayner@observer.co.uk or follow him on Twitter@jayrayner1@jayrayner1