The first row of the actual cast-on is knit with the regular sock yarn by knitting k1, y/o, thus doubling your stitches to the no. of stitches required for the pattern. A total of 5 rows make up this cast on. The process is well described in the pattern. (Although the author is Dutch, the pattern on Ravelry is available in English.)
And then you grab a pair of scissors and snip off the provisional cast on.
And finally, here are photos of the completed sock:
Two more pairs of sock projects on the needles. One pair, a simple knit sock with a small cable on each side for my "faux" nephew to be knit in the car and a more complicated design by Monika Eckert of Klabauter Wolle, recipient not decided on as yet.