Once all of my pieces were cut out (I used two pieces batting) I lined them up and "quilted" them. Unlike the instructions I was following, I had one inch hanging over on each end and decided to only make three seams in the middle.
I had a bit of difficulty interpreting the pattern and accidently sewed the lining to the top and bottom of the outer material before pulling out those seams and sewing them to the sides correctly.
After getting the side seams sewn correctly I turned it right side out. At this point I stopped following the instructions because I wanted all finished seams inside the muff. I pinned the top fabric, the handle, and part of the lining together and sewed it from the inside, leaving only a small opening to be hand whipped or top stitched closed.