You start with your usual nine patch, keeping your patterned fabric in the four outer corners and a focus fabric in the center. Cut the block in quarters, again as you would for a traditional nine patch.
Measure the quarter squares above and cut out four additional squares of the same size. Layer them on top of your quartered nine patch (above).
Mark the diagonal in each layered square, making sure you do not draw the line through the little (red) squares underneath. Sew 1/4 inch on either side of the marked line.
Cut along the drawn line, creating 8 blocks. Press the seams.
Arrange the blocks, as shown below, such that a repeating pinwheel pattern is created.
If you begin with 4 inch squares in the first nine patch, you will need 5 1/2 inch squares in the second step. Your finished block will be 9 inches square. If you begin with 5 inch squares in the initial 9 patch, you will need 7 inch additional squares in step two and will create a 12 inch square final block. Enjoy!