Vegetarian eaters are a tribe that breaks down into different layers like a soil sample. There are the veterans with their dog tags and the hunted look in their eyes at the memory of a baked bean lasagne or other unspeakable food atrocity. There is the growing band of part-timers, the veggie-curious, helping out when the movement is busy, tossing the tofu burgers into the basket alongside the Supervalu sausages.

This month will see the noisiest cohort, the vehemently vegetarian and vegan, shout loudest, or at least in the bubble that is the food universe as it flips from tooth and claw carnivore to virtuous veggie as fast as a marketeer can say “new stuff to trend in January”.

All 40 shades of vegetarian have been through the doors of Cornucopia in its 33-year history. One of the oldest restaurants in Dublin, it has been refurbished in recent years but only with a "hang up some fancy wallpaper and polished mirrors over the fireplaces" kind of approach. Compared to whole streetscapes being hollowed out a stone’s throw from here, the dolling up is a gentle update rather than a wrenching replacement.

Cornucopia feels like an insider’s place, a cosy club of people who know the drill, the shuffle up to the always-busy counter to return with your tray for one to a chair baggsied with something hand-knitted. It’s a great place to eat lunch alone. It was on one of those solo lunches that I bumped into a friend who cracked open my world a little bit more when she mentioned the upstairs. I had never been upstairs, didn’t even know there was an upstairs, which is a bit like opening the door to CS Lewis’s wardrobe and not pushing past the fur coats. The magic, for feta’s sake, is upstairs.

It’s where you can get away from the canteen clatter, stow your tray and wonder if we’ll ever, as a city, really start to enjoy these over-the-shop rooms as places to live or eat, rather than store rooms or offices. There are two levels of upstairs in Cornucopia but the middle floor is the best.

We’re here for dinner on a Sunday night, although it has more of a “linner” feel to it, that lunch-dinner that you eat early before heading to the main event. It’s partly because the hot food comes lunch style, with two side salads, so you have hot and cold food nuzzling alongside each other. The risk of melding into brown - flavour and colour - is high. It’s a feature in other veggie places.

The trick with batch-style cooking

There are small things I would change. I hate oval plates. “Oval plates say hospital,” my friend Ashe says. But what’s on them is delicious. She has the Thai-style stew, which is Thai mild. There is some coriander, coconut and lime here but none of the fire, sweetness and brothy fish-sauce (obviously a no-no) umami kick of salt, sweet and heat.

Here it’s sweet potato, cubes of tofu and a sweetly coconut-y sauce, set off with crisp green beans chopped into inches and used in almost everything on both our plates. They feature in my goulash, also, a lovely plate of fresh flavours where everything has been cooked together long enough to soften down without losing their distinctness. It’s a trick with food cooked batch-style that involves using the freshest of ingredients to start with and knowing precisely how long it should be cooked.

The salads are equally impressive. Chantenay carrots, little thumb-sized whole ones, feature in a quinoa salad that has had its game upped with a sumac and preserved-lemon dressing.

You can have wine with your meal, but we’re going with the smoothies, which fall down only by being served with plastic straws. We can drink smoothies without straws, people. Our mouths have evolved to sip liquids from glasses really quite well.

It’s back downstairs for dessert. There’s a raspberry bakewell which (ironically) doesn’t taste very baked, with more almond flavour than cake. I like it, but cakier bakewell fanciers might be disappointed. A nut-topped brownie is terrific, with proper good chocolate and great texture.

Some day we might drop the labels and “vegetarian” food just becomes food. Cornucopia has been doing it brilliantly for more than three decades. There aren’t many places where you can eat this well in a lovely room for this price. The world is wafting a new generation through its door. Long may it thrive.

Dinner for two with smoothies came to €54.

• Verdict: 8/10 The benchmark for simple hearty good food
• Facilities: Upstairs
• Food provenance: None on the chalkboard menus
• Music: None
• Vegetarian options: All there is
• Wheelchair access: 2/5 Ground floor is accessible but no toilet