This part of the blouse can be confusing and non-intuitive, but the good news is that it’s the only really tricky part. Go slowly and study the pictures. It’s worth it in the end because the technique allows you to make fully-lined short or long sleeved blouses with all the raw edges concealed.
This page of the tutorial is illustrated with pictures of a blue blouse, since I’m reusing a segment I originally wrote and illustrated in October for the My Blue Heaven retreat. After this page we’ll switch back to our holiday blouses.
Step 7 : Prepare the Blouse for Sewing Underarm Seams.
Fold the back and front of the blouse together. Pin the inner layer together.

Open up the front of the blouse and fold it wrong-side out, over the two sides of the back. Tuck the two sides of the back up inside, matching the underarm seams, but with right sides of the fabric together this time. When they’re in place, pin both underarm seams.
This part of the technique is the most difficult to explain, so I am going to show a series of pictures to show what it will look like when you have it the right way. If the explanation above is confusing, try playing around with the piece until it matches what you see.
When you have it right, the ‘sleeve’ will look like a long tube, looped back on itself.
Here are pictures of the Holiday Blouses, pinned.