Work the heel flap back and forth with two needles using 20 (22) stitches.
Row 1: *Slip 1, knit 1. Repeat from * across.
Row 2: Slip 1, purl across.
Repeat these 2 rows until flap is 20 (22) rows deep, ending with a wrong side row.
Turning the Heel:
Slip 1, knit 11 (13), slip, slip, knit, knit 1, turn.
Slip 1, purl 5, purl 2 together, purl 1, turn.
Slip 1, k6, ssk, k1, turn.
Continue in this manner, working one additional stitch before the decrease each row, until all the stitches have been worked, ending with a slip 1, k 10 (12), ssk. Do not turn.
Pick up and knit slipped stitches along the heel flap edge, plus an additional stitch or two in the corner between the heel flap and the leg, if desired, using an empty needle. Knit across the stitches that were unworked during the heel flap knitting, then pick up and knit stitches along the other side of the heel flap with a new needle. Knit half the stitches from the heel onto this needle, then slip the remaining heel stitches onto the needle with the first half of the picked up stitches.
The center back of the heel is now the end of the row. If you ended up with an odd number of stitches, discreetly decrease one back here.
Shaping the Gusset:
Round 1: On the first needle, knit to 3 stitches from the end of the needle, ssk, k1. Knit straight across the second needle. On the third needle, k1, k2tog, k to end.
Round 2: Knit.
Repeat these 2 rounds until 40 (44) stitches remain.
Knit straight until foot measures about 3.5 (4.5) inches from back of heel.
Shaping the Toes:
Round 1: On the first needle, knit to 3 stitches from end of needle, ssk, k1. On the second needle, k1, k2tog, k to 3 stitches from end of needle, ssk, k1. On the third needle, k1, k2tog, k to end.
Round 2: Knit.
Repeat these 2 rounds until 20 (24) stitches remain, then work just round 1 until 8 stitches remain.
Cut yarn, thread onto yarn needle. Slip stitches off the knitting needle onto the yarn and pull tight. Weave in ends.
Knit a second sock in the same manner.