These two-needle socks from Britain use an interesting construction. The leg and top of the foot are knitted flat, with two side flaps. These side flaps are then sewn together to form the heel, and stitches are picked up for the bottom of the foot. The top and bottom of the foot are seamed together with a seam running around the side and toe of the foot.
Weldon's Practical Needlework, Vol. 1