Thought I would give this a go.
Hook TMC 2487 Size 12
Thread - Black
Body - Callibaeits Goose Biot
1) Tie in your thread and run it down past the bend.
2) Pull off one Callibaetis Goose Biot. Do not cut it out, you must pull it off. As you do so you will notice a dark band running along one side.
3) Catch the Goose Biot in by the point.
4) Run your thread to just before the eye.
5) I prefer to use hackle pliers for this part. Wind the Goose Biot up the shank of the hook to just before the eye. You want to do this in touching turns. Do not over lap the biot or you will ruin the effect.
6) tie it off and build up a nice bulbous head.
Fly is Finished. It's up to you if you wish to varnish the head, I don't bother and I am sure the Trout don't mind either.