I measured the front of the bodice between the top and bottom piping to get the length of the placket. I wanted it to be about 50mm wide. I would be using the drill covered by top fabric.
I cut double width layer of the top fabric 2omm longer than the placket length to give a 10mm seam allowance. One length was a selvage edge, so I wouldn’t have to neaten the edge to stop it from fraying. I made a pocket with the top fabric to slide in the drill layer, which cut was slightly smaller than the placket measurements. I trimmed the edge that would be caught in the seam with pinking shears.
I slipped stitched on the fold and along the selvage edge to hold the placket in place. I then stitched the top and bottom edges in place so that there was less chance of the placket getting ruffled up and out of place.
Haha! now no one will be able to see my red and white corset. Hmm.