3.1 Using a sharp pencil or an erasable marker, draw a diagonal line from corner to corner on the wrong side of 24 of the White 3-1/2” squares. Don’t be slap-dash about the line; the accuracy on the next step will depend on this line being truly corner to corner. (Spoiler alert: you will be doing this with ALL the White squares you cut, so if you’re on a roll you can draw lines on all of them, then pull out 24 of the 3-1/2” squares for this clue.)
3.2 With RST, place a White 3-1/2” square from the previous step on one end of a Blue 3-1/2” x 12-1/2” strip, making sure the drawn line is oriented as shown.
Sew on the drawn line. (I usually sew just a thread or two toward the outside corner of the square, to allow for the thickness of the thread and the fold-back that you’re going to do. This is the equivalent of a scant 1/4”.)
3.3 Fold back the white triangle.....
...and press, using the base of the Blue strip to match the edges exactly, and maintain the 3-1/2” x 12-1/2” measurement.
Pull back the white triangle, and trim the seam to approximately 1/4".
3.4 Repeat with the remaining 23 Blue strips and marked White squares.
Total units: 24, measuring 3-1/2” x 12-1/2”
That’s it! I said it wasn’t going to be difficult, didn’t I?