Steaming bowls of pho are everywhere you look in Vietnam, from humble street stalls to upscale hotels. But Pho Thin, on tree-lined Lo Duc in the historic French Quarter, offers an unusual take on the ubiquitous noodle soup. Its reputation stems from an innovation owner Nguyen Trong Thin made when he opened the cafe in 1979. During the post Vietnam-war era, food was rationed, so the former painter hit upon a way to add new flavour to standard pho.

Classic pho has four ingredients: clear stock, quickly boiled beef, rice noodles and herbs or green onions. While every shop has its own secret recipe, few tinker with the rest of the preparation. Thin, however, decided to stir-fry the meat with garlic before adding it to the soup. This seemingly minor change completely transforms the flavour. “We didn’t have much to eat. But I still thought making good food was an art,” says Thin.

Heaped with aromatic shreds of meat and delicate green onion, what is typically a gentle broth becomes a richly layered, garlicky dish with hints of smokiness and caramelisation. Locals further customise their pho with liberal doses of lime, pickled chillies and hot sauce made in-house, and use sticks of fried dough (quay) to soak up the aromatic broth.

At lunchtime, so many people squeeze on to the wooden benches inside the narrow room that you often have to order a bowl then eat it in the cafe next door. But despite its success, the family-run shop has changed little: pho costs 50,000 dong (around £1.50) a bowl, the clientele is predominantly local and the decor no-frills.

• Pho Thin, 13 Lo Duc, Hanoi