Step 7: Sew on all the longer black and white strips, making sure the black ends meet at the corner. This makes the shadow.
Step 8: I have them lined up in five stacks of six blocks, so I can keep the original color-block layout.
Of course, that got mixed up when I had to rip out a couple of seams and add those blocks back in out of order. Fortunately, I had taken a picture early on of the order, and enlarged it and printed it out so I could see how they were supposed to go, once I had all these seams pressed open.