"We only use jian (sodium carbonate or soda ash) to neutralize the sourness during the leavening process. This allows the subtle fragrance of the flour to come out, which cannot be achieved with yeast or baking soda."

Kong says the cooking philosophy behind Xibei Super Roujiamo is summed up best as "freshly cooked meat and newly baked buns", and he adds that this is not usually the case at many other roujiamo vendors and stalls where the fillings tend to be pre-made or reheated, rather than being cooked on the spot using fresh ingredients.

"To stir-fry on the spot is the key," the chef says. "The essence of Chinese flavors lies in the wok, rather than an oven or anything else. So, to achieve a great wok flavor is very important."

To prepare the fillings hours ahead or to reheat them without the "breath of the wok" in the kitchen will lead to the food losing its taste and aroma, he says.

Instead of scooping the fillings into a round flatbread split open on one side, Xibei's roujiamo is triangular, and it's around two or three times the size of an ordinary round Chinese burger you normally find. What a surprise it is, then, when Xibei serves up its roujiamo, the large triangle is cut into two halves, and diners get to grab two smaller triangular burgers.

"We made it into a triangle, not just to stand out and appear attractive, but also because we found it is easier to eat with our fillings than a round one," says chef Kong.

Kong says customers have to wait around eight minutes for one serving of roujiamo cooked to order in the kitchen. And he says that the waiting time is acceptable to customers at Chinese fast food restaurants, but may not be at Western ones like McDonald's and KFC.

Soup dishes are a great accompaniment to roujiamo, such as hot and sour potato noodles (suan la fen) in chicken soup (19 yuan). The chewy, glutinous texture of the thick sweet potato noodles is a unique creation, while the chicken soup stewed with bamboo shoots and mung bean sprouts is another popular choice.

At the hands of the chefs at Xibei Super Roujiamo, these famous Shaanxi snacks have undergone something of a transformation, reshaped into delicacies that are as satisfying as they are surprising to eat.