I suggested a metal fabricator because it looks like he's considering a glass surface on it. Glass doesn't flex, so it'd need a pretty rigid frame under it. Not having a post or leg would mean the frame would have to be very rigid and have enough surface to attach firmly to the wall (presumably lag bolted into the studs). Any decent metal shop should be able to fabricate something like that pretty easily.
There are different ways to do this depending on the look one wants. And the materials used. And the size
One way is to build a 2" (or whatever thickness you want) wall where the desk is and trap the back edge of the desk in it.
So the desk can't go down or up at the back as you push down on the front. Think of a keyboard tray the principle is the same.
This also gives a place for your recess in the wall.