Cutting it this way gives you enough to fold it across your casserole twice.
You end up with two openings opposite each other in the middle of your fabric.
Pull the fabric through one of the openings, and us a pencil to push out your corners.
This is me trying to show you that my arm is going through the middle of the pocket, but I have short arms so you can't even see what I'm doing. But look at that gorgeous fabric! It's very important to iron it flat after this. It will make putting everything together much easier.
Next you will cut four pieces of fabric the length of your casserole (13") to use as side panels. You might also want to use two layers of batting without the insul-bright for these as well. Sew them right sides together leaving a small opening where you can turn them out. Insert your batting, get it to lay flat, and then stitch it closed. I did this at the 'bottom' of the panels because they will be inserted into your large panel that you made first and the stitching won't be seen.
Now, insert your insul-bright and batting if you are using it, into the large panel, and straighten it out. Then, without sewing it up, insert your side panels and pin together with the seam folded under.
See this? This is what you have to do. Trust me, pinning is the best thing to do. Now, carefully using a zigzag stitch, stitch the layers together, closing up your side openings. I quilted a simple diagonal from corner to corner on each panel, and then a straight line where the panel will fold up and over the casserole dish to make it a little sturdier.
Put your dish inside and be proud of what you've accomplished! Now if only I could figure out how to make one of the really nifty ones with handles...maybe I'll try that next.