This one was a breeze!
NB: You HAVE to mirror the diagram if you want your block to look like Jane's.
Print or trace the diagram (MIRRORED!) onto your foundation paper, cut apart the sections on the seam lines, and number them. (I changed the numbering a little after making the block.)
Foundation piece the individual sections. Remember to leave a ¼" seam allowance all the way around each piece.
Sew the little squares to their corresponding rectangle pieces, checking the diagram to make sure you orientate them correctly. (speaking from experience here)
Complete the block. It doesn't get much simpler than this.