Mook cakes are a Chinese pastry. You'd probably only see one at a real Chinese bakery although I understand they're making their way into the frozen section of some grocery stores.
This links to some pictures of they look like:
https://www.google.com/search?q=moon+cake&espv=2&biw=1374&bih=677&source=lnms&tbm=isch&sa=X&ved=0ahUKEwizu9_2uZTPAhUM9WMKHeDiBoQQ_AUIBigBThey're kind of like jelly doughnuts in that they come in many different flavored fillings. There's a story behind the Moon Festival and moon cakes. I don't recall the details--ah wikipedia!
"Ming revolution[edit]
There is a folk tale about the overthrow of Mongol rule facilitated by messages smuggled in moon cakes.
Mooncakes were used by the Ming revolutionaries in their effort to overthrow the Mongolian rulers of China at the end of the Yuan dynasty. The idea is said to have been conceived by Zhu Yuanzhang and his advisor Liu Bowen, who circulated a rumor that a deadly plague of "Hóuzi chuánwěi jíbìng de" was spreading and that the only way to prevent it was to eat special mooncakes, which would instantly revive and give special powers to the user. This prompted the quick distribution of mooncakes. The mooncakes contained a secret message coordinating the Han Chinese revolt on the 15th day of the eighth lunar month.[3]
Another method of hiding a message was to print it on the surfaces of mooncakes (which came in packages of four), as a simple puzzle or mosaic. To read the message, each of the four mooncakes was cut into four parts. The resulting 16 pieces were pieced together to reveal the message. The pieces of mooncake were then eaten to destroy the message.[4]
Many view the mooncake hidden messages to be a precursor to the modern day fortune cookie. By adding the covert element to the myths of the fortune cookie some have found more meaning behind the simple treat. This led to the act of removing and replacing the fortune inside without breaking for an added bit of good luck." - source Wikipedia
https://en.wikipedia.org/wiki/Mooncake#Ming_revolution