It is quilt as you go. The corners are not mitered. I merely lap each strip over the previous one (sew and flip). The result looks MUCH harder than it actually is. The exact shape of the triangles cut off does not matter, but all 4 should be the same. You can do it with random scrappy strips, but I prefer it this way. I have probably made 20 quilts (18 for babies) with this method. Each one has been a hit. Some panels work well for this pattern, but I generally use large scale overall prints. I made one for a friend's DGGS. He would not nap without it.
I did one without the corners being cut. It was boring.