Alyn Williams at the Westbury, Mayfair

It's often worth wondering what's the difference between a good restaurant and a great one. Yes, with regards to the food you can point to careful sourcing, clever techniques, and impressive presentation. The service should be on-point, attentive without being overbearing, full of knowledge about what's being served and giving the impression they'd like nothing more than to sat down enjoying the same experience with you (although never literally doing that - there's nothing more cringeworthy than front of house pulling up a seat to take your order). Surroundings should be condusive to enjoyment - not necessarily plush and frilly, but appropriate - not too loud, not too hushed, comfortable. But halfway through a meal at Alyn Williams at the Westbury I realised what may be the most important factor of all, that separates the merely good with the genuinely great. But before I get to that...

...here's what a meal at Alyn Williams at the Westbury looks like. It begins with snacks, seafood crackers topped with caviar, and dainty tubes of chicken liver parfait, both of which demonstrating some remarkably nimble-fingered work in the pastry department.

Mini arancini had another supremely delicate crust and a lovely truffly interior...

...and these little tartlets, boasting yet more impressive pastry work, containing cottage cheese and a tasteful arrangements of micro summer leaves. One of the joys of going to restaurants like this is the flurry of bitesize delicacies that appear soon after you sit down, a kind of overture of the chef's favourite techniques and flavours before even the first stated menu item arrives. These snacks were technically impressive and rewarding of flavour, a theme that would continue throughout the evening.

The first menu item proper was this crab tartlet, an absolute little blinder of a thing. Another impressively dainty pastry case was loaded with a kind of almond gel, a disc of mousse made from brown meat and sweet potato (the sweet potato element thankfully very much underplayed), and then a pile of white meat topped with almond. Almond and crab is not the most obvious pairing in the world on paper, but something about the milky nuttiness and the seafood really clicked. It probably helped the crab was very good quality, as well.

Sorry about the terrible photo of the next course, but actually, in contrast to the presentational fireworks on display elsewhere on the menu, visually this didn't promise much despite the use of a nice big scallop shell. But good lord, the flavours - suddenly grapefruit and watermelon is my new favourite thing to have with scallop, and with a yoghurt "snow" to bind all the fruit and seafood together, this initially unassuming dish became something otherworldly.

The next course came in two parts. First, a plump Cornish prawn glazed with something sweet and clever, hung with woodsmoke and tasting absolutely like the best prawn I've eaten all year. It's worth noting that although AWatW (as nobody is calling it) has a supreme command of the most cheffy techniques in the book (see next picture), they're happy to sit back and provide minimum intervention when the main ingredient does enough work by itself. The food here is clever, and tasteful, but never overthought or stuffy.

A prime example being this, at first glance just an ordinary shot glass of prawn consommé. Except it wasn't, because this, unadorned, undressed, presented with little fanfare, ended up being one of the greatest things I've ever tasted in my entire life. It's almost impossible to describe just how much flavour they'd managed to distil into this tiny amount of liquid. The main flavour is prawn, of course, except only the very best element of the prawn, the fatty, glossy seafood freshness, clean and refined and borne (presumably) of a great deal of time and care. There was a hint of tomato in there as well, perhaps some summer herbs, who knows - who cares - this was an absolute masterclass, and it utterly floored me. After overhearing us jabbering on for a good five minutes about how good it was, they brought us another one each, which in my mind makes them eligible for a knighthood. Services to the seafood industry or something. Amazing.

A blinding white chunk of halibut arrived next, and was also basically unimprovable. The fish was meaty and dense, topped with what they called "crunchy caviar", which I think had nuts and breadcrumbs mixed in as well as some seaside succulents. The sauce came in two stages - first a hazelnut and brown butter one, which was absolutely as good as that sounds, and secondly a deep-green parsley, firstly sitting neatly alongside it until I began attacking the fish in earnest, whereupon the two sauces swirled around each other quite beautifully.

The only individual item in the entire meal that wasn't the absolute best it could be was this lobster tail, usually a £17.50 supplement, which I'm afraid was a touch over and slightly mushy. Not enough to completely spoil it, but given how everything else had been cooked literally perfectly it stood out a bit. Anyway, the separate chunks of lobster, basil, oyster leaf and tomato on crispbread were great, the bisque had a great deep flavour, and anyone willing to leave me with a whole tin of caviar to attack at my own speed wins all the brownie points I have to give. So no harm done, really.

Pork jowl was so soft it practically dissolved in the mouth into porky essence, the carrots giving it a bit of structure and girolle mushrooms adding an extra foresty note.

'House salad' was a bewildering number of seasonal vegetables set into a kind of savoury jelly, which I found more technically impressive than rewarding but which my friend declared her favourite course of all (apart from the prawn, obviously).

Hake was I think an interloper from the A La Carte, which AWatW had shoehorned into our tasting menu to just make absolutely sure we didn't leave without feeling painfully on the edge of splitting open. It was gorgeous, of course - flaky and fresh, with a golden crisp edge draped with lardo and topped with a mound of Australian summer truffle, another masterclass in seafood cooking.

Next, the final savoury course, neat slices of bright pink Herdwick lamb, surrounded by seasonal veg and finished with one of those glorious sticky reduced sauces, all of which would have been enough to enjoy by themselves. But the fillet came with a little bowl of slow-cooked shoulder, with an unbelievably rich flavour and soft, velvety texture, topped with a handful of my favourite potato product, pommes soufflés. Every element of this dish, like so much of what had come before, was perfectly cooked, beautifully presented, and a tonic for the soul.

Lemon sorbet next, hiding bashfully under a kind of lemon gel blanket, all of it full of citrus flavour and far too easy to eat.

And finally, some jewel-like compressed strawberries, with a flavour so intense they could have been manufactured by Haribo, on a bed of set custard/panacotta and topped with a candied shiso leaf. A colourful, vibrant and technically impressive way to end a very, very good meal.

Alyn Williams at the Westbury is, I discovered after breathlessly posting That Prawn Consommé on social media, many people's favourite London restaurant. And clearly the meal I was served on this baking hot July evening (but don't worry, they have air conditioning) is enough to land it amongst the city's Modern British fine dining greats - the Ledbury, Core, even the Ritz which although can boast more gold fittings per square inch has the same meticulous approach to sourcing and technique. But all these places have one more thing in common other than the ability to knock out a good tasting menu - they've all been under the same, unswerving stewardship of one person for many years. This is time most other chefs would use to put in place a solid team and move on to other projects but if you go to the Ledbury, Brett Graham will cook for you. At Core, Clare Smyth. At the Ritz, John Williams. And here at the Westbury, night after night, you will find Alyn Williams, doing the job he loves with a team he's immensely proud of, serving some of the very best food in town. For the very best chefs, cooking for paying customers is not a means to an end, it's the end goal. And that's the difference between a very good restaurant, and the truly great.

9/10

I was invited to Alyn Williams at the Westbury and didn't see a bill. Many thanks to Chloe at Sauce PR for sorting.