The interfacing or fusible method toverly describes is a lot like Lori Holt's method. I'm not wild about it because I can never get the interfacing to not show somewhere along the edge when I turn it right-side out. But some people love it.
I use freezer paper underneath, leaving a small seam allowance that I baste under before appliqueing. It takes some time to do the basting, but I find it works best for me. I don't do a lot of applique these days as my hands aren't as flexible as they used to be.
I've looked at that oak leaf block myself and am thinking I might avoid it if/when we get to it. :-)