I have always used the Hershey recipe on the back of their cocoa package, but I am low if not out of that. I have plenty of dutch process cocoa I have used for cake batter, is that an acceptable sub? I'm not even sure what the difference is, I bought it because that's what my cake recipe calls for.
Will it be fine in chocolate buttercream?

yuppers and it is so much better too.

Thanks, I was just researching the difference. Should I stick with the Hershey BC recipe or is there a better one out there?

I don't know. I really like Toba Garretts recipe. It is kind of involved, but really good. It does whip up into a strange fluffy texture at first, but if you leave it alone it calms down.