Tutorial under construction.
Warning. Batting doesn’t have the warp and weft structure of cotton fabrics, and stretching the batting will cause deformation. If grossly deformed, re-cutting may be necessary to restore original dimensions. If handling pinned fabric causes the diagonal line to misalign with corner tip, sew from tip and reacquire the line as soon as possible. if, at the end of the diagonal, the line is misaligned, depart from the line and sew to the corner tip.
Image #1. Cut two 10″X10″ fabric squares and two 9.75″x9.75″ battings squares.
Image #2. Place a fabric right side down and place a batting on top, aligning all edges equidistant from edges of fabric. Absolute symmetry of the spaces around the edges is not necessary. Pin together at 12 o’clock and 6 o’clock. Draw diagonals lines from corners to corners. Stitch on the lines. I usually begin the seam in 1/4″ from a corner tip, stitch forward a few and backstitch a few. At the other end of the line, I stop 1/4″ from corner an d backstitch a few. Complete process on other fabric.