Lay a thread base with the Danville 70 Denier Flymaster Plus, ending deep in the bend.
Tail(Shuck): lay the Z-lon Baetis Olive on the near side of the hook and let the torque of the first wraps carry it to the top. Adjust, then bind up and back down to trap any loose fibers. Cut the shuck fairly short.
Abdomen: soak the Turkey Biot Baetis Olive in water first (an hour is ideal, ten minutes helps). Cut the tip off and set it with the transparent side down and the hairy opaque side up for the hairy, segmented emerger look. Tie in longer than needed with two loose wraps, slide it back so the biot's end sits a little past mid-shank, then tight wraps. Unspin the thread flat, build a smooth tapered underbody, and leave the thread at the two-thirds point.
Wrap the biot forward; it will want to fold on the first turn, and letting it do so sets the correct orientation. Grip it with fingers or hackle pliers and press the back of the biot with a finger on every wrap to keep the segments even. Stop just past the two-thirds point, several wraps to secure, cut off, and cover the stub with thread.
Strip a stem on a Medium Dun Saddle feather one size big for the hook and tie it in on the near side of the hook.
Make the post from thread: hold a finger out over the fly, take a wrap over it to form a loop, then one wrap round the hook. Repeat twice more for three loops, then two wraps round the hook to secure.
Hold the loops in your other hand and wrap the Hackle up the loops as you would a parachute. Fold everything over to check length: the hackle should end right where the eye starts. Then wrap the hackle back down the post; at the bottom, lean the post back and forth so the last turn seats at the base without trapping fibers. Tie off by sneaking a few wraps between the stem and the barbs around the post, cut the excess, secure, and leave the thread at the base of the post.
Dub a thin noodle of Dark Baetis and, holding the hackle out of the way, build the Thorax a little rounder than usual; the rounder thorax is what splays the hackle when it is pulled over.
Split the hackle fibers so they fall either side of the thorax and pull the post over. Three wraps of thread over the loops, fold the loops back, and a few more wraps to hold them.
Cut the loops off close and whip finish, catching any thread that didn't cooperate. Spread the hackle out with your fingers and trim any errant fibers.