It's really cute so I thought that I'd share my find. The plot:
The girl gets chocolate cast boyfriend's penis replica for the Valentine's Day. First reluctant, she accidentally inserts it too far and can't get it out, forcing her to wait for the chocolate to melt down. As she's getting more and more excited, she decides to give her boyfriend "special" hot chocolate when he returns.

Source: https://www.pixiv.net/artworks/79478964