I used to overlap the two pieces, cut with a slightly wavy line, then sew together by hand. It worked great but was time consuming. Then I tried using a fusible interfacing, and that was not fun either. Finally I tried zigzagging by machine with the two straight edges butted against each other, and for me that is working best. Once the quilting is done, I can't find the seam in the batting, and it is fast and easy.