Is this the technique you are thinking of? It uses a straight-line cut for the batting, but you could also use a wavy line. However, this is not for a quilt top that is already completely put together; it is for joining blocks without sashing.
https://www.candiedfabrics.com/2013/...ing-as-you-go/
Her video tutorials for it are here:
https://www.candiedfabrics.com/2014/...go-no-sashing/
A different method which I have used is to cut the batting into thirds using a wavy line. This is appropriate for completely finished quilt tops. In this case, you quilt the middle third of the quilt first. If you use this method, I strongly recommend marking your batting with registration marks along the wavy lines (so you can put the batting back together the way it was). It can also help to mark the top of each batting piece. I'll try to find some online tutorials for this method:
http://blog.ajpadilla.com/2010/08/22...-works-for-me/
http://www.mmmquilts.com/2014/02/aha-moment-tip-9.html
I originally found this method in a book by Debra Wagner. There are some tutorials on the quilt board here for this method too. I will see if I can find them. (Edit: Sorry, couldn't find tutorials with photos on the board. Just found this thread:
Quilt-As-You-Go: Pros & Cons?? )