It's very quick and easy, here's what I did:
You will need 2 contrasting sweaters- at least the sleeves, stuffing (I ripped open an old pillow for mine), and a button or some other type of embellishment.
First I took my black sweater (already just a top half) and cut the sleeves away from the collar. I tried to cut as close as I could to the collar. Then I opened them up by cutting open the seams on the bottoms- you know, the one that goes from the armpit down. Then I just stacked the two pieces I had left and cut the largest rectangle I could get out of the them- looks like it ended up being about 18" by 9"
Next I cut the sleeves from my white sweater. It is best to use sleeves that already have cuffs for this, but you could also just cuff them yourself.
Now make a sandwich with your two outside pieces right sides together and the other sleeve piece in the middle. Pin and sew around the outside with a 1/4" seam allowance. Be sure to leave a few inches open on one of the long sides, and backstitch on either side of it.
My camera battery died here, but you know the rest. Turn thru the opening you left, stuff, and hand sew shut. I like to use a ladder stitch, which I learned how to do here.
Best part- $0