Why this particular block is called "Challenge" is beyond me. It took 10 minutes to make and may actually be the quickest block in the quilt.
Surprise, surprise: foundation piecing!
Trace or print the block diagram onto foundation paper.
Number sections as in the photo.
To save time, you can piece sections 2, 3, 4, & 5 at the same time and then piece sections 6, 7, 8, & 9 at the same time.
Trim block to 5".
I used two 5" charm squares of fabric (and a teensie bit of white) for this block.