I did pretty much that, i wanted to be fast, but instead i had only Oil at the Time.
Cooked up some Oil into the most minimal as possible Butter,
once dissolved for 5 Minutes on middle Heat i added just as much Chocolate as needed so i felt it would harden just enogh later.
Like 4 Parts Choco , One Part Butter.
All worked out including the Taste beeing pretty excellent!
I would do it exact the same, took 10 Minutes, only it needs a Form to cool down, otherwise it will float into a very thin sheet (sorry English), but you can use Parchementpaper and fixate the Walls with 4 Books!! Dont let this Part out!!