Note: Contested against a published dressing: Exact article-title match, so this is the right fly, but the dressing disagrees in three roles. (1) Underbody: we store 3-4 peacock herls; the source uses UV Black Ice Dub and 2mm black foam and has no peacock at all. Source: Fly Fish Food — "Big Unsinkabeetle" (dry fly tutorial, 8 December 2020) — https://www.flyfishfood.com/blogs/dry-fly-tutorials/big-unsinkabeetle
Reference Recipe
Hook Standard dry-fly hook, 1X-long, 10-12
Thread Black 6/0 (140 denier)
Materials
Underbody Peacock ice dub (3-4 herls)
Shell/Back Black ostrich herl (1 strip 2mm closed-cell foam)
Legs Black ostrich herl (3 strands round rubber, knotted)
Indicator Hi-vis orange or chartreuse (small foam dot or Ice Dub tuft)
How to tie it
Mount the hook and lay a thread base from the eye to the bend.
Cut a foam strip a bit wider than the gap; bind its rear end at the bend so the tag points back, leaving the front free.
Tie in 3-4 peacock herls at the bend and wrap them forward as a fat underbody, stopping at the 80% mark.
Fold the foam forward over the peacock to form the shiny black shell and bind it down behind the eye; do not trim the front tag yet.
Pull three rubber legs under the body and figure-8 them so a leg splays off each side, three per side.
Set a small hi-vis foam dot or dub a tuft of bright Ice Dub on top of the shell just behind the eye so you can track it on the water.
Whip finish under the foam head and snip the front foam tag to a short blunt snout.