There’s something undeniably exciting about a restaurant residency. The impermanence of it all, knowing it will no longer be there in a couple of months, feeling as though you’re taking part in some sort of exclusive underground dining movement that is not quite radical but certainly not mainstream.

I say that. Som Saa has received a review from Fay Maschler in the Evening Standard, which is about as mainstream as it gets. But that doesn’t detract from the thrown together, off-the-cuff charm of it all.

I’d never heard of Climpson’s Arch before hearing about Som Saa. Probably because it’s a working coffee roastery right out in the sticks of east London, next to London Fields train station (not tube or even overground, an actual National Rail train station - far).

What’s particularly exciting though, is that it’s fully licensed, has a grill and wood-fired oven out in the partly covered yard space, a kitchen built into a shipping container, tables inside under the railway arch adorned with fairy lights, and occasionally moonlights as a venue for young chefs to showcase their talents.

When chefs and restaurateurs want to create a dining experience, but aren’t quite at the stage of settling at a permanent site, they’ll take up residency for a limited amount of time in a place that’s ready to roll as soon as they arrive. In this case, we have Andy Oliver, previously at Nahm (voted no.1 restaurant in Asia) and Bo.Lan in Bangkok, and Tom George, a manager from Goodman in Mayfair. Their intention is to bring the cooking of northern and north-eastern Thailand (the area known as Isaan), to us lucky Londoners. And lucky we certainly are.

Get the tube to Bethnal Green and walk north for around 20 minutes, or get a train from Liverpool Street three stops until you arrive at London Fields. Allow Google maps to instruct you from here along quiet roads and under railway bridges, as thoughts flit between I can’t wait to eat this food and am I going to get mugged if I keep parading my phone.

You’ll then either hear or smell Som Saa before you see it. Follow the murmur of music and a convivial atmosphere, or the aromas of shrimp paste and lime searing against hot metal, and you’ll soon find yourself outside a venue that by day, you wouldn’t bat an eyelid at.

The menu is brief but confident, with a handful of bar snacks, a couple of salads, four small plates, three large and one choice for dessert. Flavours are big and bold and a glorious ode to all things we love about Thai food - the salt, sour, sweetness and heat. Astringent and aromatic nectar, full of the flavours of lemongrass, garlic, coriander, shrimp paste, ginger and chillies, pool at the sides of the plates. Liquor so good that leaving a drop should come with a police caution.

The heat from the green papaya salad is penetrative rather than eye-watering, a gradual climb across the tongue to the back of the throat that will release as a little cough or hiccup. It’s wonderful, get it (£8.50).

The whole deep fried seabass, crisp and curved like the crescent of the moon, is covered in Isaan herbs and comes with roasted rice, the soft flesh a joy to peel away from the big bones of the spine (£14).

The fish also appears cured with citrus under ‘bar snacks’, with lemongrass, kaffir lime and mint, ready for wrapping in the glossy betel leaves they’re delivered on, zippy little parcels that go down barely touching the sides (£5). Grilled pork neck with chilli, lime and garlic was as dreamy as it reads (£8), and the sweet flesh of the salt roasted prawns were a great excuse to get the fingers dirty and suck on some crustacean heads (£8).

There was also a palm sugar ice cream with turmeric grilled banana which had a great warming depth (£4.50). Things that continue to flirt with me from the menu I stowed away in my bag and took home: Isaan hot and sour soup with duck leg; Northern style pork belly curry with pickled garlic and ginger; grilled fermented pork with peanuts, chill and cabbage.

There’s corrugated metal panels, a concrete floor, exposed pipes and ducts, and what seems to be a load of industrial paraphernalia stored towards the back of the space, beyond the seating - it is a coffee factory after all. But there’s also communal dining tables, Arcade Fire on in the background, a cracking wine list, standout service and some seriously good vibes.

Som Saa is so far east from where I live that it might as well be in Germany. But it’s also so good that I’m pretty certain I’ll be back. It runs until at least early 2015, with no set end date of yet. Just turn up as there’s no reservations - open Thursday to Sunday from 6pm with brunch at the weekends. See you there.

Liked lots: Huge flavours, great vibes, fantastic service.

Liked less: Please be closer to where I live.

Good for: Impressing your mates with your knowledge of London’s alternative dining scene; eating what is arguably some of the best Thai food in town.

Arch 374 Helmsley Place, Hackney, E8 3SB