I don't really remember what Hostess cupcakes taste like, but I imagine these are pretty darn close. I used the cake recipe from Post Punk kitchen. I haven't been able to find black cocoa powder, but the extra dark cocoa worked well. I also filled the cupcakes with Ricemellow, because I didn't have castor sugar on hand either.
Ganache and I have never been the best of friends. I normally think it's too thick or doesn't set the way I want it to. Instead I use a mixture of powdered sugar, cocoa powder, and enough water or milk to get it to the proper consistency. I coated the cupcakes using an offset spatula and let the chocolate icing harden for at least 20 minutes before piping the squiggles. The white piping lines were done with a royal icing and a Wilton #3 tip.
Don't mind the specks of silver luster dust you might notice on the cupcakes! They were sitting a little too close to a cake that I was decorating at the same time.