Smash the rice cake!, and just eat it!…”Kagami-Biraki”
January 11 is known as kagami biraki literally opening the mirror.
Before the New Year comes, we decorate a pair of piled round (mirror shape) mochi (rice cake) called kagami mochi (鏡餅).
They are put at toko no ma ;alcove, and/or kami dana; a household Shinto altar, and/or genkan;entrance, and so on to welcome toshi gami sama ;the Year God.
On Jan. 11, they are taken down and cooked and eaten.
It is desirable that we use a hammer not knives or scissors when we broke the rice cake because of being superstitious.
Usually we eat as o zoni; rice cake soup or o shiru ko; weet bean paste soup with rice cake.
Until the third Shogun Iemitsu Tokugawa passed away on April 20, 1651 (lunar calendar), this custom had been held on Jan. 20, but people wanted to avoid the same date (20th) in the Kanto area, they decided to do on 11th, the same date as kura biraki , storehouse opening which merchants practice.