I think this may be the technique where you copy your block onto freezer paper, cut the freezer paper along all of the piecing lines, iron the freezer paper to the wrong side of your fabrics, cut 1/4" from each freezer paper edge, then piece back together. When you make the seams, they are through the fabric only; the freezer paper edge makes it easy to make sure the seams are lined up.
I think Sharon Schamber's book on Piecelique explains the technique.