Wash and peel potatoes and grind them into paste with a scraper (a special tool for grinding potatoes). Because the ground mashed potatoes will be oxidized to red in the air, it should be washed with water several times, put more water in the mashed potatoes pot, let it stand, and then pour out the water until the mashed potatoes settle down. Repeatedly, the water gradually turns white, then filtered with cage cloth, squeezed out and put into a small pot. Add salt, pepper noodles and aniseed noodles, mix them together, knead them into small balls and steam them in a steamer for about 20 minutes. The steamed cold is dark gray, elastic and tough, which is the most authentic principle of cold closing. Some people take pains to mix some flour or starch, so that the color is whiter and the taste is not as good as the previous method. Seasoning is also very important. It is best to fry ketchup at home. If you like spicy food, add some dried peppers and oil the seasoning, which will be more delicious.