CO using backward loop.
Yarn A is Ella Rae Lace Merino, and B is Katia Bombay.
Edgings in yarn A, 4 mm needle.
Switch to 3.5 mm on first round of brioche.
I used the Purl Bee tutorial and Knitting Daily’s brioche workshop video.

Using backward loop and 4 mm needle, CO 224 sts. On first round of brioche, switch to 3.5 mm. On first round of top edging, switch to 4 mm and ktbl around. BO with 4.5 mm.

History: Before moving forward with 3.5 mm and one strand of yarn A, I had swatched with A held double-stranded and to test out different edgings (rolled St st, 2-stitch i-cord, garter stitch) and different brioche knitted fabrics with 4.5, 4, and 3.75 mm, switching which yarn would be A and which would be B. I decided to knit the cowl with 5 mm St st edge and brioche knitted with 4.5 mm.
Gauge with 4.5 mm and A held double: 19.75 sts/4”.
I worked about 3” with 236 sts on the needle and then realized I would run out of A before reaching a width I would like. So I frogged. Frogging brioche is no fun, especially when one yarn is light fingering weight and held double and I had to separate it so I could later hold it single-stranded.