Lay a thread base and tie in heavy painted dumbbell eyes about one-third of the shank back from the hook eye. Figure-8 wraps, then circular wraps under the eyes to lock them, then a drop of super glue. If the eyes can twist, they will.
Tie in a sparse clump of white bucktail in front of the eyes, then bind it down behind the eyes so it lays along the shank. This becomes the belly.
Flip the hook in the vise. The fly rides point-up from here.
Tie in 8-10 strands of Krystal Flash on what is now the top.
Tie in a sparse clump of chartreuse bucktail over the flash. The back. Sparse means sparse: Bob Clouser's originals look almost unfinished dry, and that translucency is the point.
Build a neat tapered head, whip finish, cement generously.