Here is a tutorial on making bowl, and cup cozies. I make these in several sizes. For this tutorial I will make a 6.5 inch cup cozy. I will give the measurements for 4 sizes then the directions.
Size square dart width dart length in inches
6.5 6.5 3/4 1.5 down
8 8 1 1/2 4
10 10 1 1/2 5
12 12 1 3/4 6
Cut 2 of fabric and 2 of cotton batting. It was suggested I use zap batting, I use cotton for the square size you want.Now I place the fabric and batting together and stitch an x on the square to keep the batting from moving. Do this for both sides. Fold in 1/2 and measure and mark for the darts.
Do this for all 4 sides and trim darts. Now put the 2 pieces together right sides together.
Stitch the two together around the edges leaving an opening for turning. Turn and hand stitch the opening closed. Here is the finished product. Need one for a casserole dish? Make one using the measurements of your casserole dish. The possibilities are endless.