One subtlety possibly worth mentioning is that I had the lower SB-900 set with its head rotated sideways, so as to make the area lit up on Alex's tummy longer and thinner. A surprising number of people don't seem to realize that you can do this with your flashes (or at least with the Nikon SB-600s, 800s and 900s -- and I'm betting that Canon's flashes can do the same). So it may be worth showing what that looks like:
The body of the flash still has the CLS sensor facing the camera, but the flash head is rotated around to point edgeways up. This ability to rotate the head can be handy if you're in one of those situations where CLS doesn't work unless the sensor is pointed perfectly straight at the camera.
So now basically I just had to add the pile of light. I trust no one will be too shocked to learn that was done in Photoshop :-). The first thing I did in Photoshop was to deepen the shadows even further using a Curves layer. I then used another Curves layer to strengthen the contrast of the area to be illuminated by the run-off:
I then created a new empty layer for the light, and used the Path tool to create two paths, a semi-circular one on top for the pile and a trumpet-shaped one for the run-off. I could have done that with just one path, of course, but I wanted the pile to have a softer shine and the run-off to be more concentrated. So I filled both paths with white in the new layer, but I picked a larger feather radius for the pile than I did for the run-off.
You will notice that I have also added a mask to the Light layer, covering Alex's thumb and part of her forefinger, so that the pile appears to be cupped in her hand.
The last step was to add the golden glow to the light. I thought there had to be some terribly clever way to add the glow in such a way that the yellow increased automatically as the white fell off... but in the end all I did was to select the pixels of the Light layer and then trace around its edge with a soft yellow brush (again, with a higher radius for the pile than for the run-off). (Selecting the layer's pixels first meant I didn't add any yellow to anything other than the existing light.)
The last step was to crop the image to a square format, and there you have my cover shot :-). The lighting and the post-processing were both very simple, but I am very happy with the resulting image.