I made it and still have some of it left on tap. It's fantastic as-is. In fact, I plan on making it again for the winter and dry hopping with some mint leaves.
The recipe includes 1 oz of Belgian cocoa powder but instructs you to add it to the boil. AHS sells it in the ingredients section, too. There, they recommend dissolving it in hot water and adding it at bottling/kegging. So you could either add the included powder at bottling instead of the boil, get some extra to add to the boil, or add the included to the boil and some extra at bottling.