Wash the mung beans with water first, put cold water in the pot and bring to a boil, then pour in the mung beans and cook over high heat until the soup is almost dry.

Add boiling water and cook over low heat. After 20 minutes, you will find that all the bean skins are floating on top. You can scoop them out with a spoon, cover the pot, and cook for 15 minutes. The remaining bean skins will float up again. Scoop them out again, and then add rock sugar. , after the rock sugar has melted,

it can be refrigerated.