Trying to re-create this cake but have no clue how it was paint to give it such a real square look...especially around the edges.  Any other way to get a similar look without having to paint it?  Dont think I cant do justice to it. 

https://s-media-cache-ak0.pinimg.com/736x/34/18/f7/3418f7bf466df492154edc53cf1ce2e6.jpg

I think you could use a charcoal or black dust and use a mop brush to dust the burnt look.  I wouldn't take very much at all to get it to look burnt.