The actual act of getting the chocolate into the party. I might be misremembering the method and just doing it wrong, but whenever I find a way to feed the chocolate royalty they still just melt. My method is eating the fey royalty as a male character and then using that as a workaround to feed them to a chocolate with the fuck action. I seem to remember getting a specific interaction out of this that added the chocolate to my party the first time I tried it.

Edit: I'm pretty sure it's because of a lack of feed stat after some more experimentation in a cheat save. Adding achievement points to the feed stat now and going to try and do it in a regular save.