“What are they waiting for?” I ask a spice seller, pointing at the long queue zigzagging down the street. “Moslem restaurant. Best tah-chin of Tehran,” he replies proudly.

In Farsi, tah means bottom, while chin suggests the idea of layering; tah-chin is the unpretentious, crusty rice layered with chicken that has absorbed every last drop of the warm saffron and melted butter lying at the bottom of the pan. The result is a slice of saffron goodness that is crunchy on the outside, soft on the inside and usually covered in fresh pistachios and sour barberries, which complement the sweetness of the moist, buttery rice.

Hidden in the meandering alleys of the Iranian capital’s Grand Bazaar, behind the screaming street traders selling dried figs, raw pistachios and brightly coloured hijabs, Moslem is on the first floor of a dull-looking building and, although popular with Iranians, it remains largely unknown to the growing number of foreign tourists. No one there speaks English, so I ask my neighbours in the queue if they can help me out.

A friendly Iranian family guide me through the process – declaring loudly what part of the chicken I would like, while collecting complimentary mint-and-dill yoghurt sauces sprinkled with rose petals.

At the long communal table, after being greeted as a foreigner and offered food samples by my fellow diners, a waiter brings me the biggest portion of mouth-watering tah-chin in Tehran. “Welcome to Iran!”

• The restaurant is on Panzdah-e-Khordad Street, but ask anyone at the bazaar and they’ll point you in the right direction