Step One: Allow 1 1/2" on each side of the center back skirt for this placket and mark allowance A and B.
fold line B to A and press.

Step Two: Slash down center back to placket depth, make a slash toward A leaving 1/2" for the lap.

Step Three: Turn under raw edge and whip to garmet. Make a 1/4" slash toward B and take tiny running stitches by hand or machine. I used contrasting thread for sample, use thread that matches your fabric.

Step Four: Fold B to A, stitch across end on top or underneath as desired.

Step Five: Your finished placket.