I love minky. It is for sure one of my favorite fabrics. Not necessarily to sew because it is so slippery but because it is super soft and warm. My girls will only use their rag quilts that have minky on the back.
2. Cut a piece of minky the same size. Minky is great for this because it is so wide (60 inches) So most of the time you don't have to piece pieces together.
3. Now is the part that could be complicated with a regular quilt.
Lay the quilt flat on the ground and find a couple of raggy seams in the middle of the quilt. Pin the quilt to the minky. I sew along those seams through the quilt and the minky. I do this to hold those 2 fabrics in place. If you want you could quilt a pretty design in a few of the squares. This step is not necessary but keep in mind that those 2 pieces of fabric will not be secured to each other.