Bead the curved size 12 C400 with a 3mm gold tungsten and start black Sumo 30 denier thread. Vasies picks black deliberately. A dark thread underneath makes the UV pearl rib on top read as far more reflective than it would over a pale base.
Run the thread to the bend and tie in the UV pearl ribbing material.
Dub a full, shaggy body of natural hare guard fur forward to the 65% mark. Use guard fur, not underfur. The stiff hairs are what produce the spiky silhouette this fly relies on.
Rib forward with the UV pearl material in five or six open turns and tie off, then pick the body out hard with a needle.
Spin grey partridge in a split thread and take two turns in front of the body so the barbs splay in every direction. Partridge legs are the movement element; on a big early-season fly that motion is what triggers the take.
Dub a small Pahtakorva brown opossum thorax behind the bead and whip finish.
Fish it in cold early-season water where trout are looking for large, high-calorie meals.