AWhat is the best way? Thanks
I appologize in advance for the goofiness...but the only answer that comes to mind is "you cover the cake with the white frosting"...
Not quite sure what you concieve to be the problem here, but if you're worried about the brown showing through the white frosting, I'd try crumb coating the cake first, then applying the rest of the frosting a little later. That way the surface won't be quite so dark. But still, I see no problem with white frosting on chocolate cake.
If you see the cake through the frosting... there is not enough frosting.