Wikipedia
Chatang (茶汤; pinyin: chátāng; literally "tea soup") or seasoned flour mush is a traditional gruel common to both Beijing cuisine and Tianjin cuisine, and often sold as a snack on the street. It is made from sorghum flour and/or broomcorn millet and/or proso millet flour and glutinous millet flour. The Chinese name is figurative, not literal, as there is neither any tea nor any soup in this dish.
The dish is prepared in two steps. First, flours of sorghum and/or millet are cooked in advance, often by stir-frying. When a customer orders the dish, hot water is poured into a bowl containing the flour(s) to create a paste-like mush, which is served with white and/or brown sugar and sweet osmanthus sauce (桂花酱; pinyin: guìhuā jiàng). The sweet osmanthus plant is not native to northern China.
Traditionally, the skill of the server was judged on several factors and one of them is regarding the resulting mush: the most skillful server would be able to create the mush so thick that when a chopstick is inserted into the mush it remains vertical, while at the same time the mush remains fluid. Other criteria for the servers' skills included the ability not to splash any hot water outside the bowl and spill out any flour, because traditionally all ingredients are placed in a bowl into which is poured boiling water from a special copper kettle with a long, dragon-shaped spout called 龙嘴大铜壶 (pinyin: lóngzuǐ dàtónghú; literally "dragon mouth large copper jug"), and special skills were needed to handle this equipment. The ingredients are then stirred together and the chatang is eaten with a spoon.