A single dish had filled the entire restaurant. The Tongluowan branch of the century-old Qingheyuan chain in Shanxi province's capital, Taiyuan, was packed on Jan 4.

People were lining up to savor a traditional soup with more than three centuries of history－tounao.

Wang Sanfu took his granddaughter to Qingheyuan on the first weekend of 2020 to enjoy the soup that the 83-year-old recalls first trying in 1959.

Tounao is a creamy broth made with lamb, yellow liquor, lotus roots, Chinese yams and other ingredients like Chinese herbs. It's consumed alongside marinated Chinese chives.

It's Taiyuan's most-celebrated breakfast, not only at traditional local eateries like Qingheyuan but even at the city's Sichuan and Hunan restaurants.

It's said that physician Fu Shan created the dish over 300 years ago, explains Wang Hemao. Wang is a fifth-generation inheritor of tounao-making skills, which are recognized as a provincial-level intangible cultural heritage form.

"Tounao was originally called eight-ingredient, or yimu, soup. The second name means 'to help mothers' health' because Fu created it using eight ingredients to improve his mom's health," Wang says.

It's said that Fu's mother became healthier after she started eating the soup regularly. Neighbors asked for the recipe, which Fu also shared with the owner of a lamb-soup restaurant that was later named Qingheyuan.

"It looks like a simple bowl of soup. But the process is actually quite complicated. There are at least a dozen steps."

The yellow liquor is made using millet, which takes 20 days to ferment. And the flour must be steamed for at least three hours.

Qingheyuan's tounao cooks clock in at 5 am. They first make the base with steamed flour, mutton and yellow liquor. The meat, Chinese yams and lotus roots must be pre-cooked the day before.