I heard that the cake filling is made from

This is a dumpling filled with wormwood, only very rich people can eat it

Banh tro, also known as banh gio or banh u tro, is a traditional Vietnamese cake, especially popular during the Doan Ngo Festival (the 5th day of the 5th lunar month). The cake is made from sticky rice that has been soaked in alkaline water derived from plant ash, such as rice straw, bamboo leaves, or bean husks. Thanks to the soaking process, the rice becomes soft and translucent after steaming, giving the cake a light and refreshing flavor.

Bánh tro is typically wrapped in banana or dong leaves, shaped into small triangular or long forms depending on the region. When eaten, it can be dipped in molasses or served with sugar to enhance its sweetness. Bánh tro is not only a traditional dish but also carries the meaning of cleansing the body, aiding digestion during the Đoan Ngọ Festival.