Turning the Heel
Row 1 (WS): P11, P2tog, P1, turn.
Row 2 (RS): Sl 1, K3, SSK, K1, turn.
Row 3: Sl 1, P4, P2tog, P1, turn.
Row 4: Sl 1, K5, SSK, K1, turn.
Row 5: Sl 1, P6, P2tog, P1, turn.
Row 6: Sl 1, K7, SSK, K1, turn.Proceed in this fashion, increasing by one the number of sts worked before the decrease in each row, until all of the stitches have been worked, finishing with a right side row. You should have 12 stitches on your working needle.
Divide your heel stitches in half, leaving the last 6 sts you just worked on the current needle and sliding the first 6 onto an empty needle (figure A). With the right side of the work facing you, take the needle holding the leftmost heel stitches, where the yarn is attached, and use the needle and yarn to pick up stitches all along the slipped stitched edge of the heel flap, moving upward toward the cuff, 1 stitch per slipped stitch. You should have about 12 picked-up sts, but if your heel flap was made shorter or longer than suggested, the number of picked-up sts will vary accordingly (figure B).
Now take an empty needle and continue knitting across the first needle with 10 stitches that have been "resting" all this time; then with a new needle continue across the remaining 10 resting stitches. You should now be at the other (empty) side of the heel flap, with an empty needle in your hand. Proceed down the heel flap by picking up stitches just as you did for the other side, except now you are working from the cuff downward and starting with an empty needle. Pick up the same number of sts that you did on the other side, then continue across the 6 live stitches that are waiting on the last needle (the ones remaining from the section where you turned the heel). You should now have a tube again: the two instep needles will have 10 sts each, as they have from the beginning, and two needles will have more stitches, because youve picked up all those stitches from the sides of the heel flaps.
Gusset Decreases
Now that you have a tube again, start working stockinette st in rounds, using all five needles. The needle that starts at the center bottom of the heel as you work around is Needle 1, and so on, with the needle that ends at the center bottom of the heel being Needle 4. (The fifth needle is your working needle.)
Round 1: K6, K tbl of remaining sts on Needle 1; K across Needle 2 and Needle 3; on Needle 4, K tbl until 6 sts remain, K6.
Round 2: K until 3 sts remain on Needle 1, K2tog, K1; K across Needle 2 and Needle 3; on Needle 4, K1, SSK, knit to end.
Round 3: Knit
Repeat rounds 2 and 3 only until all four needles have 10 sts each on them again (i.e., the original number of sts that you had for the cuff, evenly divided among your four needles).