I just started to do this with a large log cabin quilt. My blocks measure 12-1/2. I cut the batting 13 inches square and the backing 15 inches square. Put them together, press both sides and I did stippling. Then I folded the backing back (out of the way) and trimmed the batting even with the top block piece. I am able to put two blocks with the back sides right side together and sew right along the top block/batting edge. I then fold the top flaps (for lack of a better work) to the edge of the block top, again on the block and stitch down the side, securing the 'sashing'. I really like this method, it is quick and enables me to do another design with the backing fabric.