Preparing ECPE candidates? Try Build Up your Proficiency-Writing Skills, with 12 units on organising writing properly and developing writing skills for the C2 level examinations.
I’d suggest using it in courses of at least 40 hrs, as there’s plenty of material to cover and it can be a bit difficult for students at a low competency level. If, however, you don’t use a coursebook in C2 level courses, but only focus on exam preparation (e.g. a one-year-course), this book can prove quite useful.
Extra tip for greek EFL students: it’s a really helpful coursebook for students who find producing written speech challenging in their native language as well. I’ve used this book “backwards” with remarkable results.