...if it's good enough: just start writing. Before you do your prospectus! I just gave this advice to a really great student.
It's how it works when you write a book. You write the book first, then you write the proposal. No one in their right mind would write the proposal first...
Warning: this only really works if you're very inspired and devoted to your subject. And it still takes some digging and some reflecting. But you do that already—because you're into it.





