Start the Chartreuse UTC 70 thread and bind in a length of Clear Midge or Micro Tubing, carrying the wraps a little way down the bend. Midge tubing suits 12s and 14s; use micro tubing on 16s, 18s and 20s.
Tie in the Red Flashabou at the same rear point, wrap it forward four or five turns only to make the hot butt tag, capture it with thread and trim the excess.
Build a buggy taper in thread: wrap forward and back a couple of times over the work, each return stopping a little shorter than the last, and stop the thread a quarter of the way back from the eye.
Stretch the tubing tight and wrap it forward over the taper to the hanging thread; capture it with tight wraps and trim the excess.
Underwing: tie a pinch of Pearl Ice Dubbing in across its middle so equal parts hang front and back, fold the front half back over itself and smooth the transition with thread, then trim the underwing just a little longer than the butt of the fly.
Stack a clump of Bleached Elk about half a pencil in diameter so the tips are even, pinch it on top of the shank slightly longer than the underwing, and lock it with a loose wrap pulled tight.
Bite the thread through the fibers a couple of times to keep the wing from spinning, add a couple more wraps, then trim the butts while still holding the wing, and clean up the stubs with more thread bites.
Tie in a Brown Whiting Rooster Cape hackle right near the head, sized so the fibers reach a millimetre or two below the hook point, and trim the excess stem.
Wax the thread and dub a sparse, tightly noodled Chartreuse Ice Dubbing thorax - not shaggy, no guard hairs standing up - then take the thread all the way to the eye.
Palmer the hackle forward through the thorax in slightly spaced turns, one last wrap right at the front, capture it with thread, trim the hackle tip and whip finish.