"Oak leaf rice cake." 柏餅、かしわもち。
Round-shaped mochi filled with sweet bean paste (an) and wrapped in an oak leaf (from the Kashiwa or Daimyo Oak, Quercus Dentata, which is native to Japan). As an, both tsubuan (rough type with parts of beans left), koshian (fine type) and misoan (flavored with miso) can be used. The mochi can be plain or flavored, for example with yomogi (mugwort) as on the picture.
Popular sweet on Boys Day (Tango no Sekku, May 5) because of the symbolism that the old oak leaves do not fall off until the new shoots have grown. Is nowadays available the whole year.
The origin of kashiwa-mochi goes back to mid 18th c. Edo. They were popularized over the whole country by the system of alternate attendance of daimyo in Edo. In the Kansai and Western japan, where the oak does not occur naturally, originally on Boys Day chimaki (mochi made of glutinous rice and wrapped in a bamboo leaf) were eaten. Instead of oak leaves, here also sometimes leaves of greenbrier-type trees are used (Sarutoriibara, Smilacaceae).
In contrast to sakura-mochi, where the cherry leaf has been pickled, the oak leaf is not meant to be eaten.