Cut and stack a small clump of white calf body hair. Tie it in at the 70% mark, pull it upright, and wrap a thread dam in front to keep it standing. Then wrap up the post itself 8-10 turns to stiffen it. A floppy post makes for a sloppy hackle.
Tie in mixed grizzly and brown tail fibers at the bend, one shank length.
Dub a sparse muskrat body forward to the post. Thin noodle, slight taper.
Tie in a grizzly hackle at the base of the post, shiny side up.
Wrap the hackle around the post horizontally, 4-5 turns, each turn beneath the previous one. Tie off under the hackle wraps.
Whip finish at the head. The fly should sit body-down in the film with the hackle spread flat like a landing pad.
Substitutions
Wing post instead of White calf body hair: White poly yarn — Easier to work with, very visible; Hi-vis orange or pink poly yarn — Much easier to track in broken water; White Aero Dry Wing — Synthetic, floats better; CDC puff post — More natural but harder to see
Body instead of Muskrat dubbing: Adams Gray Superfine dubbing — Easier to dub thin; Gray rabbit dubbing — Close match, widely available; Olive dubbing — Turns it into a Parachute BWO variant
Hackle instead of Grizzly: Dun hackle — Slightly darker, still great; Brown hackle — Warmer tone
Other versions
8 more in the app: Fischer's Flies, Klinkhamer-Style Curved Body, Extended Body, Barbless, Tan, Yellow, Pink, Purple.