I just made this for my birthday and it was delicious!
I didn't use any margarine and it didn't seem to make any difference. I used Ghiradelli 100% unsweetened chocolate for the baking bar and Hershey's for the cocoa powder.
My friend who said she doesn't like chocolate flavored things found it delicious, and I can't stop reaching in the fridge for the leftovers.

Highly recommend for a delicious gluten free and vegan treat, thanks Mattie!