Complex sentence: The rice-beer cake is prepared using rice, several plants that are been ground into a paste which are mixed with cooked rice, and previously prepared rice-beer cake, which is stuffed into a vessel known as a "jamba".
Split into simpler sentences: The rice-beer cake is prepared using rice that has been ground into a paste and several plants, which is then mixed with cooked rice and previously prepared rice-beer cake. This mixture is then stuffed into a vessel known as a "jamba".