It's one of those techniques where at first you might think it won't work and then it does! Gotta love that about sewing :) Your shirt might be slightly different but this technique will be useful for most shirts with a yoke.
Below is an excerpt of the instruction booklet for the Garçonne shirt / dress it explains how to sew a yoke on a shirt.
1. Sew two rows of basting stitches, above and below the stitch line, between the notches on the back piece. Leave the tails. the gathers are specific to the Garçonne shirt / dress, but your shirt might have a small pleat, you need to secure with basting stitches.
2. Match the notches of the back piece and the yoke and the yoke facing (the second yoke piece that you cut). Pull the tails of the basting stitches to gather and use pins to secure the gathered back piece to the yoke and yoke facing. Stitch the three layers together, sandwiching the back pannel between the right sides of the yoke pices. Grade the seam to reduce bulk. Remove basting stitches.
3. Press yoke and yoke facing up and topstitch close to the seam line
4. Fold the yoke facing down. Align the shoulder seams, right sides together, of the front and yoke and pin.
5. Roll up the front and the back panels.
6. Fold the yoke facing over the rolled up fabric. Align the yoke facing, the yoke and shoulder seam and pinning as you go. Stitch, grade the seam allowance and turn.
7. Press the shoulder seams and topstitch close to the seam line. Baste stitch yoke at the neckline and the armscye inside the seam allowance at ca. 0.5 cm ( 1/4” ) from the edge. This step helps keep the layers in place when you insert the sleeve.
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