Assaggi, 39 Chepstow Place, London W2

In an unlikely room above a London pub is an Italian so authentic you need to be a native to read the menu

(JOEL CHANT)

"Do you think I should kill him now, or later?" the waitress asks. "I'm not so interested in when it happens," I tell her. "I'm more bothered about how quickly you do it." She smiles. "Don't worry. I'll kill him slowly. Slow is always better." "Was it Jacques Brel," I ask, "who said: 'A bullet: too slow; poison: too quick'?"

This exchange – she's referring to the person who accidentally wrote my booking down for the wrong day – occurs while we're barely over the threshold at Assaggi. One visitor to this west London restaurant posted an internet review complaining that the staff are over-attentive; my own feeling is that anyone who launches straight into this kind of robust banter could serve me air pie at £17.99 and I'd still go home happy.

Assaggi is a small restaurant located – somewhat improbably – above a pub near Notting Hill. It established its prestigious reputation back in the days when advertising executives still contemplated slogans like "reassuringly expensive", since when Sardinian chef Nino Sassu has sustained its popularity with his imaginative Italian menu.

The seemingly humble décor whispers sophistication, the walls hung with large rectangles in single colours. They resemble noticeboards, so much so that the less culturally enlightened diner might assume that some vengeful rival had swiped the reproduction of the Mona Lisa, and the Polaroids of regulars getting hammered that used to be pinned to them. The menu is in Italian with no translation, a practice that – since it demands the staff explain every item – gives monolingual Brits a taste of what it feels like to be blind and competing in a memory game.

I'm fortunate in that my companion is the writer Michael Rose, who lived in Florence for 25 years, during which time, besides becoming an authority on Puccini and Berlioz, he conducted an in-depth study of Italian wines and cuisine. His scallops are "as good as I've tasted" even if, for £13.90, Assaggi might risk serving four rather than three. They have removed the orange coral which, despite its powerful flavour, is regarded by some scallop enthusiasts as the bivalve's prize feature. I have prawns with fritella di risotto al limone – a seductive melange I've never encountered before, certainly not sculpted into something that resembles a gonk.

If the main menu lacks an English equivalent, Assaggi makes up for it on the wine list, whose translator seems to have suffered something of a rush of blood. Its heading reads: "A pleasure for those that recognise themselves as Lovers and Connoisseurs of the good one to drink" – a description which, as chance would have it, is Micky and me down to a T.

Last time I was here with a friend we engaged in an exhaustive tasting of the house Pinot Grigio, "a delicate and healthy wine". On that occasion my fellow Connoisseur left so brimming with health that she fell asleep on the Piccadilly Line and almost missed her flight to Detroit.

We order the white Fiano di Avellino "Vinosia" 2009 Ercolino, described as having a bouquet of "dry straw", which could equally be described as (in a good way) farmyard stable. It's an especially good complement to my fillet of monkfish which, at £24.90, I'd expected to be spectacular, yet I can only describe as perfect. Michael's generous carpaccio di manzo rucola e Parmigiano – sliced fillet of beef with rocket and shaved Parmesan – is, providing you use the best ingredients, as here, almost impossible to get wrong.

I try the dessert wine Passito di Pantelleria Ben Ryé Donnafugata on the grounds that I have not, to my knowledge, previously embarked on "a flavour trip through melon notes and dry walnuts". It offers a more complex experience than the humble vin santo I'm used to, and so it should, given that, at £9.50 for 50ml, it comes in at just under £90 a pint.

Assaggi delivers what its regulars expect: fine food with prices to match. This is, to be fair, not the most affordable area of London; the tables near us were occupied by parties from the broadcast media, who all knew each other. If you're paying for yourself, a trip to Assaggi is likely to be reserved for a special occasion. Your visit is guaranteed to be unforgettable, if only for the intimate atmosphere, the excellent service and – depending on how you're coping with the recession – the bill.

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 back 9-10 as good as it gets

Assaggi 39 Chepstow Place, London W2, tel: 020 7792 5501 Lunch and dinner, Mon-Sat. About £130 for lunch for two with one bottle of wine, service not included

Inspired Italians

Caffè Z

87-89 Goldspink Lane, Newcastle, tel: 0191 230 4981

A proper southern Italian restaurant in a residential street; hearty rustic food at reasonable prices

Enoteca Turi

28 Putney High Street, London, SW15, tel: 020 8785 4449

One of the best all-Italian wine lists in the world is the stand-out attraction of the Turi family's stalwart, near Putney Bridge

Firenze

9 Station Street, Kibworth Beauchamp, near Leicester, tel: 0116 279 6260

The Poli family's decade-old venture offers some of the most authentic Tuscan cooking outside of Tuscany

Latium

21 Berners Street, London W1, tel: 020 7323 9123

Maurizio Morelli's food is as creative as it is mouthwatering

Reviews extracted from 'Harden's London and UK Restaurant Guides 2010'. www.hardens.com