A few weeks ago I had one of the best dishes I've eaten in the Westin Hotel. It was simple dish, a scallop placed on a bed of lobster risotto, but every part of the dish was perfectly cooked and flavoured. If that were commonplace I wouldn't still remember it. The fact that I do is evidence of the rarity of a perfect dish.

If you get something that good and that memorable, there's only one obvious course: go back for more. So it was that this week I was back in The Westin looking for that Holy Grail - a perfect meal. It's been a while since I was last out with my friend Marian Kenny, so I arranged to go to The Westin's Exchange restaurant with her. Now Marian is delightful company and on this evening she looked radiant in her latest little black dress from Helen McAllinden, but it's probably true to say she's not a foodie, at least not in the same way that I am. Ordinarily that doesn't make much difference, but on this particular night it did.

If you don't know the Westin, it's main entrance is on Westmoreland Street and it occupies a space that was formerly a couple of banks. The facades are unchanged, but huge renovations were done internally. The banking heritage remains in the names, like the Exchange restaurant and the Mint bar. Their banqueting hall is one of the original banking halls, a truly spectacular monument to Mammon - high-ceilinged and stuccoed in decorative plasterwork with marble pillars and pilasters. The Exchange dining room is less splendid and runs parallel to Westmoreland Street. It's quite an awkward space, being much longer than it is wide. A partition glassed wall effectively divides the dining area into three.

We arrived into a very busy dining room and got a table at the far end, away from the two large tables of a big group, where we studied the menu. This was a large folded card on which the set Christmas dinner of €60 per head was laid out in red print on grey. I mention this small detail because it was to have repercussions. The truth is that both Marian and myself are of the age when we really ought to carry spectacles with us at all times, but vanity being what it is, we don't. As a result of this, reading the menu wasn't exactly easy in the low light, but from the fairly long list of choices Marian chose fillets of sole to start followed by seabass, while I picked the quail to start and guinea fowl to follow.

The wine list is long and varied, but you don't need me to tell that wine lists in five star hotels don't carry bargains. There were a few wines under €30, but the bulk of the list falls into the €35 to €55 range. I chose a decent Pinot Grigio, which was listed at €33. We also had two large bottles of San Pellegrino at €5 each.

With the choices made we sat back in anticipation and the first dish to arrive was an amuse bouche, a poached oyster served in its shell. It was delicious, but Marian is severely allergic to shellfish, so she passed hers to me. Shortly after this our starters arrived, a really good quail dish in front of me and a rather overcooked dish of sole fillets in front of Marian. It wasn't so overcooked as to be unacceptable, but the fish had lost its firmness and fell apart into flakes when she tried to cut it. Despite this, it tasted pretty good and Marian ate most of it.

It was when the main courses arrived that we had a problem. Marian had taken a forkful of fish and then started to gag. 'I think I've just tasted some crab,' she spluttered. Sure enough the fish was served on a bed of brown crab meat. Neither of us remembered having seen that on the menu, but when we looked at one there it was. The dish came with crab meat, alright. This was a catastrophe for Marian, who started to worry that she'd eaten enough to get an immediate allergic reaction, but thankfully it didn't materialise.

The restaurant manager couldn't have been more solicitous, offering to change the dish for anything else that she might have liked, but at this stage Marian would eat no more. Which means that this review is based only on my food, instead of the more usual two-meal judgement. Rather guiltily I ate my all of my main course, enjoying every bit of it, while Marian watched me. I know that hardly seems like the actions of a polite dinner host, but I was hungry.

Marian resolutely refused to even consider a dessert, but when the chocolate fondant that I'd ordered came she was quick enough to dig into it. It was very well made, oozing rich luscious black chocolate when opened. It finished what was in the end was a meal of two halves: mine with food and Marian's without. I asked for the bill and noticed that we'd been charged for only one meal, which I thought was a nice gesture from the house. With the wine and water it came to €103, without service charge.

Mine turned out to be a good meal, but the much hoped for perfect meal didn't materialise. Maybe like the Grail it's an ideal that will never be found, but then again, there's fun to be had in the search for it.