This heel works for any sock knit on a multiple of 12 stitches.
Divide your stitches for the heel
Divide your total number of stitches by 4
Knit the first quarter of your stitches onto one double pointed needle.
Slip the next quarter onto a second needle without knitting them.
Slip the third quarter onto a third needle.
Slip the last quarter of your stitches onto the beginning of the first needle.
The heel flap
Next row, working on the heel stitches only: Slip 1 purlways, purl to end
Next row: Slip 1 knitways, knit to end.
Repeat these two rows until you have worked the same number of rows as you have stitches in your heel. For example, if you have 36 heel stitches you will work a total of 36 rows. End having just worked a purl row (work an extra row if you need to in order to end on a purl row).
Turning the heel
Divide your total number of heel stitches by 3 and place markers 1/3 and 2/3 of the way along your row.
1st row: Knit to within 2 stitches of the second marker. SSK, turn
You will now be working on the stitches between the markers.
2nd row: Purl to within 2 stitches of the marker, p2tog, turn
3rd row: Knit to within 1 stitch of your marker, ssk, turn
4th row: Purl to within 1 stitch of your marker, p2tog, turn
Make a note of the number of stitches that you knit or purled before decreasing on rows 3 and 4. You will be working the same number of stitches before your decreases on the following rows.
For example, if you worked:
Row three: K9, ssk, turn
Row four: P9, p2tog, turn
Then you would repeat these two rows exactly
Repeat rows 3 and 4 until all the stitches to the left and right of your heel have been used up. Finish having just worked a purl row.
Knit half of your heel stitches and replace your end of round marker
Picking up stitches for the gusset
With a new needle (your heel stitches will now be worked across 2 needles), knit the 2nd half of your heel stitches and pick up one stitch for every two rows down the side of your heel flap.
For example, if you knit 36 rows for your heel flap you will pick up 18 stitches. (36 divided by 2 = 18)
Knit the instep stitches.
Pick up the same number of stitches up the other side of your heel flap.
Knit to your end of round marker (the centre of the heel).
Working the gusset
1st round: Knit to within 4 stitches of the end of needle 1, k2tog, k2
Knit across needle 2
Needle 3: knit 2, ssk, knit to the end of the needle.
2nd round: Knit all needles without decreasing.
Repeat these two rounds until your total number of stitches equals the number you first cast on.
Continue with the foot of your sock.