To create this look just pipe with a Wilton 1M start piping tip to fill in between layers like you normally would. Put a little extra emphasis on the very outer ring of frosting so that it looks really ruffled. Then stack the cakes. The top layer should be flattened out and smoothed in such a way as to leave the frill around the outside.
It is very helpful to have a spinning cake decorating tray and an off set spatula to create this effect.
I have found that the American butter cream frosting is much too sweet for this cake. Swiss meringue is the way to go. Trust me on this one I love sweet stuff and the American butter cream made me sick to my stomach on the first taste test. This was a yellow cake. There is no way that a white cake should ever look that brown on the edges. If a white cake were to be browned at all it would be over cooked.