Start by embroidering two parallel lines of stem stitch about an inch apart. Then work small blocks of three straight stitches each, horizontally across the center space, keeping them evenly spaced between the lines of stem stitch and from each other.
Then, using a blunt needle, slide through these blocks as shown. Leave the thread loose so that it curves instead of forming a sharp "V". You have to really work to keep them even (and I didn't do a perfect job of it myself).
Finally, work one French knot in the center of each circle.
I worked with aida cloth this time because it's really important that the spaces in between are even. You could use linen, too, and count carefully when you make your blocks of three lines.