Cut a strip of fabric, twice the width of the top of the sock + seam allowance and about 1 1/2 " wide.
Put the fabric right side to right side and sew up the side seams to match the width of the sock as close as you can. (I did this with each sock since it will change slightly with each one.)
With the good side of the sock on the inside, pull the binding down over the top of the sock, with the good side of the binding on the inside.
Line the top two edges together, pin the top two edges together and sew around the top with a 3/8 " seam.
Flip the whole sock right side out, and pull the binding up. Fold over the raw binding edge 1/2 an inch. Then fold it again over itself and the top raw edge of the sock.
Pin to hold it in place and sew a straight line at the bottom of the fold to secure.