Feeling nostalgic, I decided to make an attempt to create my own "peek-a-back" top from scratch.
Here's what I did ...
Step 1: Create the Front Panel
Next I took a top I know fits me really well and folded that in half (with the front facing out).
I lined up the folds and traced around top, leaving a half-inch for seam allowance.
Then I cut along the line (but not the fold) and unfolded it to get my front panel.
Step 2: Create the Two Back Panels
Then I took the top and folded that in half, this time with the back facing out.
Using a washable marker, I traced around the outer half of the top, leaving half an inch for seam allowance.
**NOTE: The top was not placed on a fold this time***
Then, keeping everything in place, I unfolded the top, and traced the remainder of the neckline about to where the shoulder strap begins (see pictures).
I drew a straight line connecting the top end point to the bottom end point.
I then cut through both layers of fabric to get my two back panels.
Step 3: Sew Together
I then hemmed along the diaganol straight edges of the two back pieces.
I connected the two back pieces to one another using a basting stitch close to the edge line.
(By "connect" I mean "sew.")