XOPP is code for one of Sydney's most memorable dishes, the one that Momofuku New York's Dave Chang called "the best dish in the world".

The one created in Sydney's Chinatown in 1990 by the now-retired Golden Century head chef Leung Yung, when he combined large, just-steamed pipis (wedge-shaped clams) with a thick, pungent, house-made XO chilli sauce. XOPP, get it? (You may have to say it out loud.)

XO pipis are still the Golden Century's best-seller, and have now lent their name (sort of) to the new baby in the Century family; delivered by Billy Wong, son of Golden Century's founders, Linda and Eric Wong.

Inside Kengo Kuma's bravely round Exchange building at Darling Square, the 160-seat restaurant sits like a doughnut around an open atrium aflutter with a kinetic art installation.

It feels as if it should revolve, but doesn't. Tables are set with pops of colour – celadon green bowls, tangerine chopsticks, orange water glasses – against an industrial concrete-and-pipes background.

The surprise here is that the new custodian of the XO pipis, head chef Zachary Ng, isn't hand-picked from the Century kitchens, but instead grew up in Japanese-inflected seafood fine-diner, Sepia. So this will be interesting.

And it IS interesting, the menu carefully blending Golden Century favourites (salt-and-pepper squid, roast duck, Singaporean chilli crab) demanded by regulars, with more contemporary dishes such as prawn mantou rolls with XO mayonnaise, kung bao Glacier 51 toothfish and jasmine bubble tea panna cotta, for a new, younger audience.

To kick off, a glass conserving jar of smooth, rich chicken liver parfait seems out-of-place until you realise it's flavoured with Shaoxing wine and accompanied by crisp Chinese donuts ($14). That's fun.

There's a tension between the old and the new here, but out of that tension comes some memorable moments. Of the new, roasted lamb breast ($36), flavoured with coriander seed and served with a thick soy bean sauce and lettuce leaves for wrapping like bo ssam, is a keeper.

Of the old, an aromatic hotpot of beef tendon, brisket and daikon ($38) is comfort food at its finest.

But I want my pipis. You can do 500 grams for $46 and 1 kilogram for $88 – and for another $10 have them sent out on a bed of fried vermicelli noodle (a must). And They Are Good – big, fleshy, A-grade shells, lightly steamed open and tossed into a thick, heavy, garlicky, vegetal, spicy sauce that soon seeps into the noodles below, turning them into a dish in their own right.

A supposed "vegetable" dish of brussels sprouts with pork cheek ($24) is more meat than greens, and typhoon shelter cauliflower ($9) – its fried garlicky, spicy topping usually reserved for shellfish – feels a bit dry and boring.

But it's a treat to have steamy, treacly, ma lai gao ($10) on a dessert menu and not just at yum cha.

It's hard to know where XOPP will land, once it stops spinning in what must be a difficult Gravitron-like site. Three private rooms are yet to be completed, there is no discernible reception, the cocktail bar is still a work in progress and at this early point, service runs from sweet to shambolic.

But the centre of gravity, for diners at least, remains a simple but satisfying dish of pipis in XO chilli sauce.

The low-down

Vegetarian: A scattering of choices, but beware, most vegetable dishes come with seafood or meat.

Drinks: An impressive, hard-working, 250-strong wine list overseen by Jon Osbeiston, intuitively heavy on the chardonnay and pinot noir, with the key to the Golden Century's mammoth cellars as a bonus.

Go-to dish: Stir-fried pipis with XO sauce, $46/$88 (fried vermicelli, $10).

Pro tip: Order too much and take the leftovers home for tomorrow night.

Terry Durack is chief restaurant critic for The Sydney Morning Herald and senior reviewer for the Good Food Guide. This rating is based on the Good Food Guide scoring system.