I’m thoroughly enjoying Anne Campbell’s Zigzag pattern in New Directions in Sock Knitting! The heel flap and gussets are worked simultaneously with the instep.
It’s hard to show in a single photo, but gusset stitches are increased on each side of the heel flap, and a few stitches are increased in the center of the flap. These stitches will be decreased as the heel is turned through a series of short-rows in the usual manner. That means that there are no gusset stitches to be picked up — ingenious!