Open the lid to cook the skin and close the lid to cook the filling. When the lid is open, the water temperature is not very high and the skin is cooked, while when the lid is closed, the temperature is high and there is a lot of steam, which cooks the inner part of the dumpling, i.e. the filling. It's like cooking noodles, you can put noodles in the water at about 70° because you don't necessarily need a high water temperature to cook pasta, but the dumplings are filled with meat, so it's not easy to cook them, and the temperature is high when the lid is on in order to cook them through. Vegetarian dumplings in the pot after the opening of the lid to cook the good, frozen dumplings should always cover the lid to cook, keep stirring, dumplings after freezing the water in the dumpling skin will be lost, it will become dry some, it is not easy to cook, so to cover the lid to cook.