Start with an eight and a half inch square of fabric. Turn it inside out and pin up one side.
Sew up one side using your sewing machine. The turn the fabric and sew up the other side about three-fourths of the way up. Turn your fabric right side up and finish sewing.
Iron the square flat. Then fold down the sides to make a smaller square.
Fold and iron the sides down. Sew down all the points in the middle.
Sew two squares together in the middle.
Place a two and a half square in the middle of the two larger squares. Pin down in place.
Fold the sides down and hand sew them.
Now you have a cathedral window pane.