Ok quick question, i was thinking of making chocolate buttercream but have a plain buttercream recipe i really want to use and maybe just add in the cocoa. My question is do i just add in the cocoa to tasting or will this make it too stiff or should i take out some of the icing sugar and substitute with the cocoa?

When I add cocoa powder to my buttercream, I add a couple more tablespoons of water with it so it's not so stiff.

thanks