Vietnamese rice noodle soup, bun bo hue, is pretty much the perfect thing to eat on a sweltering afternoon, especially if you’re into lemongrass. Traditionally built on beef and pork bones, it’s complex, tart and hugely fragrant, and just fiery enough to get your internal air-conditioning system pumping without blowing your skull off.

Think of it as pho’s sexier, spicy cousin. Marry pho. Kill minestrone. Go home with bun bo hue and cover yourself in shrimp paste.

The best versions can be found in the soup’s home city of Hue in central Vietnam, but there are plenty of Sydney bun bo destinations worth crossing town for, such as Song Hy in Canley Heights, Cabramatta’s Dong Ba and Haymarket’s Gia Hoi. Meanwhile, Cash Only Diner might be the only restaurant in Australia with bun bo hue and rare bottlings of the French herbal liqueur Chartreuse.

Cocktail professionals Chau Tran and Bryce McDonough opened Cash Only in 2020 after moving their CBD basement boozer, Burrow Bar, to another CBD basement. The new site came with an upstairs dining room, and turning it into a casual Vietnamese restaurant seemed like the right idea.

With exposed brick, bottle-lined shelves and yawning arched windows, the space could also be a coffee shop in New York. (And, yes, you can pay by card. The name is a nod to all those hole-in-the-wall noodle shops where you can’t.)

True happiness comes from eating bun bo hue with a margarita or bourbon-spiked Vietnamese iced coffee

Tran’s mother was born in Da Nang, near Hue, and the menu is inspired largely by her home-cooking recipes, such as com hen clam rice ($24.50). Working with chef Bobby Nguyen, Tran combines baby clams with pork rinds, puffed rice paper and a picnic’s worth of pickles, and a pungent mixture of clam broth and fish sauce can be added to taste.

“Mumma Tran’s” profoundly crunchy cha gio pork spring rolls (three for $18) are equally layered with texture when wrapped in lettuce leaves and vibrant green mint.

But back to the bun bo hue ($22.50). In Hue, you might expect to eat it at an outdoor market, sitting on a plastic stool, sweat pouring down your face and back. It will likely be bobbing with a gnarly pork knuckle or two, and a purple wodge of coagulated pig’s blood. At Cash Only, it teems with deboned and rolled pig’s trotter instead, plus peppery pork loaf sausage and floppy swatches of beef shin. There will not be blood.

However, there will be hypnotic levels of lemongrass, spice and tang, and chewy strands of spaghetti-sized vermicelli. Add bean sprouts, lime juice and assorted soft herbs at leisure, and temper the building heat with something from the cocktail list.

With all respect to the pleasures of Hanoi Beer ($12), true happiness comes from eating bun bo hue with a cold margarita ($22.50) or bourbon-spiked Vietnamese iced coffee ($20).

A small selection of wines includes a highly drinkable 2021 Inkwell Mataro Rosé from McLaren Vale ($17/$77) that loves a betel leaf-wrapped bundle of minced beef seasoned with anchovy sauce (five for $22).

Tom chien com prawns ($20 for four) are coated in green rice flakes that are all snap and crackle, and slow-cooked pork belly is chilled, sliced and grilled to make unctuous skewers powered by a glaze that stars savoury-sweet caramel sauce thit kho ($12).

These are riveting snacks, but there are a couple of kinks, too. Cubes of black-peppered beef on the bo luc skewers (three for $23) are much tougher than they need to be and the floor staff are friendly but not always informed. On one visit, we’re told the fish of the day is a whole flounder swimming in ginger and chilli ($48) and overcooked barramundi lands on the table instead, with no explanation.

Desserts made by chef Bryan Zhu are a riot, though, particularly a bowl of vanilla and coconut panna cotta covered in a rainbow of mango, lychee, strawberry and pandan cream ($17).

I should also mention that a lot of the menu can be ordered downstairs at speakeasy-style Burrow Bar until 11pm – great news for anyone keen on a late night of deeply aromatic soup.

But Cash Only’s bun bo hue always tastes better when the sun is shining, when you can grab a table by the window, ask for extra chilli, and welcome the onset of Sydney summer. Traditionalists just need to bring their own blood jelly.

This review was originally published in Good Weekend magazine