It’s surprisingly taxing, being this restaurant reviewer’s dining companion. You have to work for your supper. No “It’s delicious”, or “Mmm, tasty”, will suffice. I need you to pin meaningful, specific words and phrases to your general impressions, such as, “Smells like an oven that needs cleaned”, or ‘Too much truffle oil”. Those companions who cook and/or bake regularly always distinguish themselves from mere eaters who like or dislike a dish, but can’t put their finger on why exactly. The acid test, of course, whether we’re talking active cooks or passive eaters, is this: “Would you happily pay for this with your own money?”

This question sweeps away any notion that it is impolite to criticise a free meal, instead cold calculations concentrate the mind. The active cooks are much more reluctant to part with money for restaurant food unless it’s something they can’t or don’t make at home. They assess a dish more forensically, for technique and ingredient quality. The passive eaters, bless them, are content with pretty much anything because they lack the confidence to assess what’s on their plate knowledgeably. Instead they’ll focus on something that is peripheral to the food: service, decor, atmosphere. Here they feel their opinion is more legitimate. “How was Restaurant X? What did you have?” I’ll ask them. “Can’t remember much, but our waitress was nice”, is one classic response.

And when I’m reviewing with Sumayya Usmani, the brilliant food writer and teacher of this parish whose sophisticated palate for flavour is second to none, tasting prowess goes right up a gear. Few people have her ability to decode flavour, to identify its component building blocks, to understand the methods that brought it to the table. Here in Non Viet Hai in Glasgow’s West End, sibling to the successful Non Viet in the city centre, the pair of us are judge and jury. Sumayya? She’s ready to be pleased, but no pushover. We agree, as she puts it, that too many restaurants “try to be too ethnic but don’t know how to handle the ingredients”. Yet we both give a thumbs-up the chargrilled mango squid. Tender, probably through marination, prettily criss-crossed, it carries the alluring scent of the grill. Its salad- matchsticks of raw courgette, carrot, and under-ripe mango, generous coriander and enough chilli to give the fish a kick- brings freshness. Its dipping sauce has a mustardy undertow that adds complexity.

We turn to the ground pork in betel leaves, grilled to a crisp. Betel is a hard flavour to describe, for me, its slightly floral, yet earthy. It puts Sumayya in mind of dried angelica leaves. (As I said, this woman’s flavour map and memory are phenomenal.) The hot, little, meaty rolls are served with cold rice vermicelli, roasted crushed peanuts, and another terrific salad: soft lettuce heart combined with shredded julienne vegetables, in a lime juice, palm sugar, fish sauce dressing that shows the assurance of a native cooking from instinct and experience.

We puzzle over the ‘shaking beef’, so soft each fibre of its being seems to have dissolved into a sponge. How do they get the meat so tender and yet still pink in the middle? Sumayya cracks it before me: a long marinade that features rice wine, soy, perhaps, and a searingly hot but brief toss in the wok. We’re disappointed with the banh xeo, Non Viet Hai’s rendition of the Southern Vietnamese savoury fried thin crispy crèpe. It’s filled with a crudely cut stir-fry that’s over-reliant on thick slices of red pepper and spring onion, and although the fried tofu tastes milky and fresh, the vegetables have an unpalatable oiliness to them that even the fresh mint leaves, salad, and invigorating dipping sauce that flank the bahn xeo can’t cut. The same unedifyingly greasy oil smell hangs around the ‘mango spring rolls’. Nothing special we agree, probably tinned mango slices, deep-fried in off-the-peg wrappers.

We agree on our final verdict: not bad at all, but could be better still. Oh, and if I was a reviewer of the passive eater type, I’d add that our waiter was exceptionally helpful.

Non Viet Hai, 609 Great Western Road, Glasgow 0141 334 3090

Dinner: £20-30

Food rating: 8/10

Joanna Blythman is the Guild of Food Writers’ Food Writer of the Year 2018