It is lotus root starch. Mix the lotus root starch with cold water. After the water for cooking the lotus seeds boils, pour the prepared lotus root starch evenly into the boiling water. Stir it quickly with a spoon to avoid lumps. It’s best to stir while pouring. You can also add longan, hawthorn, and fresh fruits. For example, you can put an appropriate amount of sugar into the soup with chopped oranges, grapes, apples, and pears...Be sure to press the lotus seeds in a pressure cooker before making the soup, and peel the longan.