I have made 2 king size cathedral windows quilts and I sew the blocks together before I fold the last flaps to the center of the block. I press the final folds, then open them up and use the crease as the sewing line to sew 2 blocks together. when I get 2 rows sewn together, I attach the 4 corners and then I use a blind stitch to sew the window fabric in. No stitches show on the back side of the quilt. Only the seam line where the blocks are sewed together.