I grew up in an autonomous region of China called Xinjiang; the food there is different from the typical Han cuisine. One of our famous local dishes is mutton soup, a simple bowl made of mutton and potato.

My mom still cooks it every now and then. It’s an easy comfort soup: just add enough water to cover the fresh mutton, toss in some common spices, such as pepper and cardamom (草果 cǎoguǒ), and cook for about two hours. Keep it uncovered and the smell will fill your home with warmth.

We usually eat the soup with nang (囊), a kind of salty bread. Tear the nang into chunks and let it soak in the soup. Now lower your head, drink thirstily and devour the mutton with your right hand—in Xinjiang, it’s customary to eat with your hands.

This was my very first soup. It warmed my stomach and my heart on chilly Xinjiang days. But mutton soup is only popular in the northwest of China. In the southeast, in Jiangxi Province, every day starts with chicken soup.

Cantonese, believing soup is the most nutritious meal, drink liangtang (靓汤) all year around. In Shanghai, the soup might be plain (maybe just tomato and egg, or seaweed and cucumber) but it’s considered a mandatory part of the meal, while in Beijing the soup is always saved for last

But for Zhao Xin, the 36-year-old head chef of Hai Fu Wan Restaurant, a soup demands more than just eating. It demands principles. “Be honest with yourself, and be honest to the soup that you make,” he said. “That’s what my shifu (师傅, master) taught me.” His shifu also taught him to make a Tan Family soup with 100 years of history.

At the end of the Qing Dynasty, fast food dominated Beijing eateries; easy Manchurian meals, like thinly slice, hot pot mutton (涮羊肉 shuài yángròu), were the standard. One gourmet, the Guangdong-born official Tan Zonghou, fought the trend. He frequently invited friends over for slow-cooked meals, using delicate flavors, fine ingredients, and very unique tastes. His Stewed Chicken with Soy Sauce and Clear Chicken Soup combined traditional Guangdongcuisine with local Beijing flavors, and—because the hoi polloi couldn’t even try his foods—his dinner parties became those of legend. It was initially referred to simply as Tan Family Cuisine (谭家菜), but the more formal name was guanfucai (官府菜), the Official’s Cuisine. And, at a low-end price of 480 RMB for a meal, it remains a taste for the elite.

So why not learn to cook it at home?

Chef Zhao agreed to teach me one of his simpler recipes: clear mushroom soup. He comes from a long line of Tan Family chefs—his great great-grandfather was the first—and he’s been cooking it for 16 years. He’s considered a master in the style. And this dish takes only 11 hours to make.

“What? What soup needs 11 hours?” I asked, shocked.

He gave me a big smile. “My mushroom soup is based on the old clear soup recipe, which demands eight hours. You can cook it in just one or two hours, but—as my shifu said—the soup knows if you’re being honest with it.”

Now I wouldn’t want my soup to doubt my honesty, but why spend so long on a bowl of soup?

“My soup is as clear as a cup of tea,” he pressed. “There is not a drop of oil floating in it. There’s no strong smell, just a slight scent of chicken. The first spoonful warms your throat, the second warms your stomach. Some gourmets consider my soup the ultimate pleasure.”

He was already seven hours into a batch for the restaurant, and his white uniform was dripping with sweat. He didn’t care. The only thing he seemed aware of was the huge, boiling pot of broth. He lifted the lid, skimmed the oil off of the top and laughed. “I started to prepare this soup yesterday. It’ll be ready in half an hour. The key is the temperature—look at the tiny bubbles on the surface. They’re called yuyanpao (鱼眼泡, fish-eye sized bubbles). Turn down the flame, and make sure the soup bubbles like this for eight full hours. This is the secret of my soup.”

There are workarounds. “You can use a pressure cooker, and shorten the time to two hours. You will get the same soup, eventually. But your tongue will know the difference.”

This soup may be an investment in time, and in materials (“Remember, always buy the top quality vegetables. Only these can match the soup.”), but once you take your first spoonful of this ancient Tan Family recipe, your tongue really will know the difference.