Cast off edges are together, right sides up. We will call the lower piece "front," since it will be closest to you while you work, and the other "back."
On front, bring your yarn needle up thru the center of a "V".
On back, insert needle to side of "V" and come out the other side.
On front insert needle thru the same hole you started in, and come out thru the center of the next "V."
Continue alternating the last two steps...
...and you'll get this. I worked the second half of the row in a matching color so you can see how well it blends.
And from the back it looks like this.