Cut a strip of razor foam roughly as wide as the hook gap, and match your thread colour to the foam you have chosen.
Start the thread on a size 20 dry fly hook at about the 70% point, taking a few extra securing wraps because nano silk wants to slide off bare hook. Trim the tag and wrap back to the point above the barb.
Measure one shank length of foam, hold the strip against the near side of the hook and take two or three wraps; it will roll itself upright on top as you tighten. Leave the rear tag long for now.
Build the segmented body: pull the foam back, take three or four wraps forward, then one or two securing wraps, and repeat up the shank. Pull hard on the first segment, less on the next, and not at all on the last, so the body tapers.
Tie the foam off an eye length behind the eye, pulling it just tight enough to draw it forward, then lift and trim. Now trim the rear tag into an arrow point to form the shuck.
Fold a three or four inch length of 6x monofilament into a loop, align the tips and snip them even, then bind the loop on top of the shank right at your thread position and back to the foam. Pull it rearward first so no mono hangs over the eye, and build only a slight thread base underneath.
Strip a light Dun rooster saddle hackle so you have about twice the bare stem you need, tie it in dull side up, and wrap forward and back a few times to lock both hackle and monofilament in tight. Leave the thread an eye length behind the eye. Sizing the hackle slightly oversized gives the fly a better profile on the surface.
Hold the monofilament loop upright in one finger and wrap the hackle up the loop, keeping everything tight, going up about the length of the body you have left, then wrap back down through the hackle. Wrapping up and back is what makes the stacker thick and durable.
Bring the thread back to the tie-in point, secure the hackle stem with a few turns and snip it out of the way with fine-pointed scissors.
Pull up on the monofilament loop, sweep the fibers back, and pull the loop down over the top. Take a few loose securing wraps on the mono behind the eye, then pull down on your thread as you draw the loop forward to tighten the hackle upright.
Snip the monofilament away, keep the hackle fibers held up and out of the way, and finish with a four-turn whip finish.
Other versions
2 more in the app: Fly Fish Food Tie, variant 1, Fly Fish Food Tie, variant 2.