"When mentioning Chang'an City, people often remember the name of Yangtang", which is the nostalgia of the ancients for the food of Chang'an (now Xi'an). Nowadays, there is a metaphor that "If you don't taste beef and mutton soup, you haven't been to Xi'an", which is the praise of the food of Chang'an by modern people. "30 million Qin people roared Qinqiang together, and a bowl of mutton soup made them happy", which is a vivid portrayal of Shaanxi people. There are many versions of the origin of beef and mutton soup. This article selects two of them: one is that in the second year of Emperor Suzong of Tang Dynasty (757 AD), the Tang army and the borrowed "Daqin" army quelled the "Anshi Rebellion". With the permission of the emperor of the Tang Dynasty, some "Daqin" soldiers were allowed to station in Chang'an. When the "Daqin" soldiers marched and fought, they often carried a kind of food called "Ermu" similar to "Nan". The march and battle lasted for a long time, and the "Ermu" carried by the soldiers often became dry and hard and difficult to swallow, so they soaked it in mutton soup, which was the prototype of "Pao Mo". As the exchanges between the "Da Shi" soldiers and the locals became more and more frequent, the method of making "Ermu" also spread from the military camp to the market, and over time, it became today's "Mo". For more than a thousand years, after the continuous development and innovation of Muslims in Xi'an, "Pao Mo" has been greatly improved and enhanced in terms of color, fragrance, taste, shape, etc., and has become an excellent delicacy that everyone from high-ranking officials to ordinary people likes to eat. There is also an interesting legend: Before Zhao Kuangyin was successful, he lived in poverty and wandered on the streets of Chang'an (now Xi'an). One day, he had only two pieces of dry Mo on his body, which were too hard to swallow. Coincidentally, there was a mutton shop on the side of the road cooking mutton, so he went to beg for a bowl of mutton soup so that the Mo could be soaked before eating. Seeing his pity, the owner asked him to break the Mo into pieces and soak it in a spoonful of boiling mutton soup. Zhao Kuangyin took the soaked Mo and ate it in big mouthfuls. He felt hot all over, sweat on his head, and his hunger and cold disappeared. Ten years later, in 960 AD, Zhao Kuangyin was crowned emperor and established the Song Dynasty. He was known as Emperor Taizu of Song. During a tour in Chang'an, Zhao Kuangyin passed by the mutton shop and smelled the aroma. He could not help but think of the time when he ate mutton soup and steamed buns ten years ago. He stopped the car and ordered the owner to make a bowl of mutton soup and steamed buns. The owner was flustered. The shop didn't sell steamed buns, so what should he use to soak them? He hurriedly asked his wife to make some pancakes. When the pancakes were baked, the owner saw that they were dead (unfermented) flour and not well cooked. He was worried that the emperor would get sick after eating them, so he had to break the steamed buns into pieces, pour mutton soup on them and boil them again, put a few large pieces of mutton on them, carefully prepare the seasonings, and then serve them to the emperor. Zhao Kuangyin praised them after eating them, and ordered his entourage to give him 100 taels of silver. This matter spread like wildfire and spread throughout Chang'an. As a result, more and more people came to the shop to eat mutton soup and steamed buns, and then it became a unique snack in Chang'an. Su Dongpo, a great writer in the Northern Song Dynasty, once wrote a poem praising "Long cuisine has bear bacon, Qin cuisine only has mutton soup". The cooking technique of beef and mutton soup is very strict, and the process of cooking meat is also very particular. The beef and mutton are carefully selected, and the meat and bones must be separated. When cooking, boil the bones first. Put the bones in a pot of clear water and stew over high heat. After two hours, foam will float. After skimming, put the old seasoning bag to enhance the flavor, then stew the meat, and finally replace the new seasoning bag to add flavor. Press and cover with a meat board, burn over high heat, and make a bang. Then, stew over low heat overnight. When you wake up, the whole house is full of mellow fragrance. When you get up, you can see that the soup is fresh and rich, its color is like milk, and the aroma of the ingredients is fragrant; the meat is lean and soft, and the fat is not greasy, without any smell of mutton. The steamed buns used for beef and mutton soup are specially made, nine-tenths of flour and one-tenth of yeast. Mix, stir, and knead. Make a steamed bun with two liang of dough and one edge, and bake it in a pan. It is called beef and mutton soup, but it is actually boiled bun. Boiling bun requires considerable skills. The heat must be right and the ratio of soup to bun must be inappropriate. Pao Mo can be divided into four types according to the cooking method: dry Pao (no soup), soup (a mouthful of soup left after eating), water siege (more soup) and single walk (eating bun and drinking soup). The soup is determined by the bun, and the soup is seasoned with the soup, boiled quickly over high heat, and served in a bowl at the right time. That mouthful of soup is eaten to the end, and there is only a mouthful of soup in the bowl. Dry Pao, no soup in the bowl. Water siege, the bowl is surrounded by soup and the middle is bun. When eating Pao Mo, break the bun into pieces the size of soybeans and put them in a bowl, then ask the chef to put a certain amount of cooked meat and original soup in the bowl, and add shredded cabbage, garlic sprouts (or chopped green onions), fungus, chrysanthemum, vermicelli, cooking wine, salt, MSG and other seasonings, and make it with a single spoon. When eating, choose the right position, eat carefully, and avoid stirring to keep the freshness and original flavor. If you add hot sauce and pickled garlic, it will have a different flavor. Xi'an Tongshengxiang Restaurant was founded in 1920, and it has been nearly 90 years. It is a national catering company, famous for making beef and mutton soup. The characteristics of Tongshengxiang Restaurant's beef and mutton soup are "heavy ingredients and mellow taste, rotten meat and thick soup, smooth steamed buns, overflowing fragrance, and pure taste". It has a complete and strict operating process from material selection to production, and the craftsmanship is very particular. Therefore, Tongshengxiang Restaurant's beef and mutton soup is the only flavor snack in Xi'an that has won the highest national award "Golden Tripod Award" and is recognized as one of the "Top Ten Cultural Symbols of Shaanxi". Tongshengxiang Restaurant is the first company in Xi'an's halal catering industry to go out of Tongguan and cooperate with Beijing Hotel to open a branch in Taijichangkou, Chang'an Street in 1991. "The most delicious yokan is from Tongshengxiang" is the sincere praise for Tongshengxiang's beef and mutton soup steamed bun. Tongshengxiang's "beef and mutton soup steamed bun" making technique is not only an intangible cultural heritage of Xi'an, but also included in the Shaanxi Province Intangible Cultural Heritage List in May 2007; in June 2008, it was included in the second batch of national intangible cultural heritage list.