When I first started making quilts, I would make the backing a little larger than the top, and then roll it over to the front and hand stitch it down. Now I Sew my folded 3 to 2 1/2" strip onto the back first and roll over to the front and stitch it down using a walking foot, folding the strip up forming a diagonal, and then straight down to make my mitered corner. I have looked at tutorials online to figure out the best way to do this. The one I have never tried, because of my lack of a large table, and no desire, is the envelope method.