To make a cosy to fit an approximately 13"x9" casserole, you will need:
1/2 yard of fabric for the outside
1/2 yard of fabric for lining
1/4 yd. fabric for the flap
1/2 yard Insul-bright material
2 yards of webbing for the handles
2 complementary buttons
The Cutting: Out of your outside fabric, cut one piece that measures 14"x15," and one piece that measures 14"x14." Out of the lining fabric, cut one piece that measures 14"x15," and piece that measures 14"x14." Cut these same size pieces, one each, out of the Insul-bright material (I think that a piece of felted wool would probably work as a good substitute for the Insul-bright). Out of the flap fabric, cut 2 pieces that measure 8"x14."
Preparing: Now, match the 14"x15" outside fabric piece with the same size Insul-bright piece, and baste together using a 1/4" seam, with the Insul-bright facing the wrong side of the fabric. Repeat this procedure to attach the other Insul-bright piece to the 14"x14" lining fabric. Then take your webbing, and pin it in place onto the 14"x14" outside fabric piece, as below. Place the webbing about 3 1/4" from each side, with about 4" of fabric between. Stitch the webbing in place as shown below, stopping your stitching about 2 1/2" from the side, and stitch a square with an X for reinforcement, as shown.
Now you are ready to assemble: Pin and sew each piece right sides together, according to the diagram below (make sure when you sew the handled piece that the handles are places so they come out the sides that are not sewn to the other pieces, and make sure not to catch them in your seams).
Now, press your seams open and lay your long rectangle out on the table. Next, flip each end piece up onto the matching piece so that the two lining pieces are right sides together, and the two outside pieces are right sides together. Turn back about one inch at the top to match the edge, and pin, as shown below:
Sew around the three pinned edges, using a 1/4" seam. Now you are going to square off the corners so that your casserole which has some height will fit nicely into your carrier. Grasping a corner from the inside, match the bottom and side seams, and pinch together, which will result in a triangle at the end, like this:
Pin, and measure 1 1/2" from the point, and make a line.
Stitch along this line, flip right side out to see a squared corner, then turn it back to the wrong side and trim the seam to about 1/4", like this:
Repeat this procedure for the two corners in the lining section, and the remaining corner in the outside section. Now, fold your rectangle in half, so that the right sides of the flap material match up. Measure 3" in and down from the top flap-seamed edge, making marks as shown:
Using a ruler, connect the marks with a straight line. Sew along this line from the top of the flap towards the edge, stopping about 1/4" from the edge. Pivot, and stitch down the edge, stopping about one inch from the bottom. Repeat for the other side of the flap.
Now, turn the outside fabric pouch right side out, along with the flap. Press these out to get a crisp fabric. Take the lining pouch, still wrong side out, and insert it into the outside fabric pouch. Match the turned under open edges, and pin. It should look something like this:
Topstitch around the top flap, down the sides of the flap to close the small opening, and around the top of the pouch opening, thus enclosing and finishing all raw edges. Now, all you have to do is insert your casserole, fold the flap over and mark where your buttonholes and buttons should go. Sew them up, and you're done!
***Important: While this is an insulated carrier, it does not mean that you should set this on your lap with a hot dish inside! The carrier will keep your food warm, but it will not protect your skin from the heat of the dish!