FIRST: I started with cutting off both sleeves and traced my hand print on a piece of paper. NEXT #2: I cut out two pieces of flannel, stitched around the hand (right sides of the flannel together) leaving the bottom open and stitched the top of the sleeve in a hand shape. My first attempt at the flannel lining I made the opening the size of my wrist and was too small to get my hand in- I recommend making sure it is wide enough for the widest pair of your hand.
Step #3: I then cut around the stitched top part of the sweater leaving a 1/4 to a 1/2 inch seam allowance. I folded the bottom opening of the flannel lining up and hemmed/ finished the edge. Step #4: Stuffing the flannel (right sides together) into the sweater (right sides out) I stitched the flannel to the sweater using a zig-zag stitch. I didn't want the lining falling out every time I took the mittens off.
And TA-DA.. a new pair of warm winter mittens.