Start the Brown UTC 70 thread and tie in a short length of White UNI 6/0, binding it back to the bend.
Wrap the brown thread forward as smooth and even as you can, stopping at the thorax about a third of the shank behind the eye.
Rib the body with the White UNI 6/0 in evenly spaced open turns up to the thorax, capture it and tie off.
Tie in a narrow strip of Dun Medallion Sheeting on top of the shank at the thorax.
Dub Grey Superfine sparingly, just enough to coat the thread, and build a round, bulbous thorax in two or three small applications rather than one thick one.
Take the thread to the eye, pull the Medallion Sheeting over the top of the thorax and lash it down. Trim leaving a short stub hanging over the front.
Cut the stub in half and split it down the middle back to the thread (with hackle pliers on a seam, or the scissors), then lash one half down along each side of the fly.
Whip finish. Trim each wing pad just longer than the wing case and round the corners; give the larger side a haircut to match.