Start the yellow body thread on the size 18-20 Maruto D04 and run it back to the bend.
Tie in a sparse Coq de Leon flor de escoba tail, a little longer than the shank. Stiff, splayed barbs are what hold the back of a tiny dry fly up in the film.
Build the whole body from the yellow thread itself, wrapping forward and back to a fine taper to the 65% mark. That is the skinny in the name. At size 20 any dubbing at all would fatten the silhouette past what a selective fish will accept.
Tie in two natural grey CDC feathers as an upright wing over the thorax, tips about a shank long.
Take a few figure-of-eight turns at the wing base to stand it up and split the flotation across the two feathers, then whip finish a minimal head.
Fish it during small yellow dun hatches on flat water, dead drift and drag-free.