We were removing the 17 layers of old wallpaper in the kitchen for a repaint and discovered the wallpaper was holding a good portion of the plaster around a window in place, which proceeded to crumble away when we removed the paper. This is an exterior wall and it appears to be brick covered with what I'm assuming to be brown coat, then a finish coat was applied to that. Anyone have any suggestions as to how to repair this to get a fairly even surface that we can paint? Drywall compound? Clean/wet, add another brown coat, then finish that? I'm sure getting this all to level with the wooden frame around the window won't be easy either. Pictures attached, we are at a loss, thanks!