Knit across the instep in pattern (this is needle #1).
Row 1: At the beginning of needle #2, slip the first stitch purlwise, *k1, sl 1 until one stitch remains. Slip this last stitch.
Row 2: Turn work, purl across heel.
Repeat these two rows until the heel is your desired length. The one for this sock is 17 rows. End after finishing a purl row.