Start the brush as normal, stroke the fibers of quite a long hackle to a 90 degree of the stem and than put over the core thread as normal.
As you wind the dubbing and the hackle together lift the under thread and natural the thread on the upside a bit from the dubbingblock so the hackle can also turn. The dubbing is dark possum and the hackle a black hen hackle. I think that a hackle from the saddle is even better.
I think the pictures speak for themselves.
Here I lift the brush a bit from the dubbingblock.
Greeting
Ruard