It occurred to me that I might be able to help someone by sharing my instructions for lining the hood of the Somerset Hoodie. I didn't photograph as I went, so I don't have a photo tutorial. But this method worked well for me:
1. Cut two hoods, one exterior fabric and one lining fabric. So you should have four hood pieces, plus the long hood trim piece.
2. Sew/serge together the center seam of each hood, one in exterior fabric and one in lining fabric.
3. Serge/finish the bottom edge of the hood in lining fabric. Set that hood aside for now.
4. Sew the shoulders (front and back shirt pieces), as in Mama Stellato's instructions.
5. Sew the hood in exterior fabric only to the shirt, as in Mama Stellato's instructions.
6. Press the long hood trim piece, wrong sides together, as in Mama Stellato's instructions.
7. Sandwich the hood trim piece between the exterior fabric hood and the lining fabric hood. The right sides of each hood should be together, with the hood trim in between. The edge of the hood, where you will sew, has four pieces of fabric. It works best to start in the center of the hood, with the center of the trim piece, and then work your way down to the bottom of the front pieces. Pin, then sew. Finish edges, since they'll show on the shirt pieces below the hood.
8. Turn hoods so that exterior hood is on outside, lining on inside, and trim where it belongs. Press carefully. Below hood, press finished edges to inside of shirt.
9. Topstitch. Make sure topstitching extends down below hood, stitching finished edges of front pieces to inside of shirt.
10. Topstitch at base of exterior hood, catching lining hood.
Presto, a nicely lined hood.