I would make this in two separate pieces.
First, make the cape and the tall collar. A pattern like one of the following may help you get the cape and collar shapes:
That collar is pretty specific - you'll need to do some modifications to any pattern you use to get the height and the long lapels.
For the second part, the clasp, make a separate triangular shaped piece. Attach it (either permanantly, by sewing, or by a button or other attachment) under the cape collar on either side of the cape front opening.
Pictures and tutorials from my costuming portfolio at Syagria's Cosplay Site!
Star Trek Original Series Uniform!
Original Creation for AB13
Most Recent Con:
PAX East, Anime Boston 2013