DIY Cathedral Window Pillow with a difference

I tried my hand at making a Cathedral Window quilt pillow; it looks lovely, but—being a bit of a perfectionist—I’m not entirely happy with how the corners come together (I imagine many people feel the same way, given how often buttons are sewn over that spot).

Also, because I wasn't careful enough, the raw edges of the grey fabric are peeking out in places—something I’d really like to avoid. You can prevent this either by not placing any fabric underneath at all (which I don’t want to do, as I find it too boring if the "frame" matches the background color) or by coming up with a different solution. 

 So, I brainstormed ways to add color to the background without having fabric edges show through, while also saving myself half the ironing work.  

I took a few photos along the way, in case anyone wants to try this themselves. 

For a 40 cm x 40 cm cushion, you need a 40 x 40 cm base area and the corresponding squares—I opted for 5 squares, so each one had to be 20 x 20 cm. Cut the pieces slightly larger (I used 23 cm x 23 cm) so you can neatly press the edges over. 

Cut the fabric and press the edges to create a 20 x 20 cm square, then mark the center—do this by drawing two lines across the entire square using a fabric marking pen.

Press and mark all the squares accordingly. 

Set the center square aside (it is only in the picture because I was testing the color combination) and first sew the outer squares in place with long stitches along the markings (I secured them beforehand with temporary spray adhesive).

Then fold back the corners pointing toward the center in order to sew on the center square, again following the lines.

Then press all the corners inwards, making sure the outer corners are precise; the center isn't as important, as it won't be visible later.

...and cut squares for the filling—slightly smaller than the base (mine are 13 cm x 13 cm)—and iron the squares onto the base using Vliesofix.

Then, just as with a standard Cathedral Window quilt, fold the edges inward to form curves and stitch them down.

Done! Now just attach a back panel to your liking (I chose an envelope closure), insert the filling, and the cushion is finished.