Does it have to be yellow? If not, I'd make chocolate ganache. It doesn't get much easier than this:
16 oz bittersweet chocolate pieces
16 oz heavy cream
Heat heavy cream til frothy, pour over chocolate, let stand 2 minutes then combine thoroughly.
Bring to a touch cooler than room temp then whip it into a frosting. People will be amazed at how delicious it is.
I run the Frontier Wholesale co-op in February, May, August & November