Start bright yellow thread on a #16 curved shank hook and run a base back to the bend.
Tie in about eight cream hackle fibers as a tail at least one body-length long, angling them slightly downward so they will sit in the surface film. Bury the butt ends forward rather than trimming, there is not enough material to make a step.
Bring the thread back to the rear, wax it, and dub a thin sulphur yellow body forward to about the 65-70% point. Keep it slim, mayfly bodies are thin.
Cut a strip of plastic bag about a quarter inch wide. Stretch it gently until it necks down slightly, then fold it over on itself two or three times so you get a little bow tie shape with a flat pinch point in the middle.
Tie the bow tie in at the front of the body by the flat middle, then take figure-eight wraps front-to-back and back-to-front to set the two wings out to the sides, spent-style rather than posted upright.
Trim the wings roughly to length, a little above where the hackle tips will reach.
Tie in a slightly undersized cream or light ginger hackle just behind the wings. Take two wraps behind the wings, then about three in front of them.
Tie the hackle off, sweep any forward barbs back and take a few wraps to make a flat landing area for the head.
Whip finish, then snip off the excess feather and any stray barbs crossing the eye. Add head cement if you like.