That looks like a flooded glace icing -- Sugarshack shows that technique in her latest DVD on sheet cakes.
what is glace icing? how is that different from royal icing- or is this a difference?
It's different than royal icing -- there are several recipes around for it. I'm not particularly a fan of it for a lot of reasons, but if you look in the cookie forum it's very popular. It dries firm but not rock solid like royal.
it almost looks like they filled the pan with chocolate and then flipped it out onto the pan. maybe only fill the pan 1/4 inch with chocolate. that would be my guess.