This is a relatively standard re-skim. However the chimney breast had been removed previously and the plaster wasn't flush with the two sides. 

So first of all I gave the whole wall 2 coats of PVA, to make the new plaster stick properly, then, I had to fill the middle out so the wall was level right the way across, and finally skim the whole lot perfectly flat.

Dont worry it is only a minute long.