Caveat: I live in the Midwest, which is why I think every bride needs a casserole carrier. It's quite possible that people outside the Midwest don't carry their casseroles as far afield as we do. (Do people outside the Midwest even make casseroles?) We've raised the potluck to an art form.
I made the pattern up as I was going along, but my grandma had a carrier similar to this. It's basically a quilted rectangle with ties at the corners to wrap it up around the casserole dish and handles that wrap around the underside of the casserole to support it. The major benefit I see to this design is the corner ties, which allow the carrier to be folded flat in the napkin drawer on those rare occasions when people are bringing dinner to your house instead of you to theirs, and the continuous handles, which add some stability.
1/2 yard of fashion fabric
1/2 yard of lining fabric (I used quilting cottons for both)
2 yards of double-fold bias tape in a coordinating color
2 yards of handle webbing
2-3 inches of velcro
Ribbon for corner ties
A walking foot for your sewing machine is really helpful, but not totally necessary
Masking tape or a quilting seam guide will make it easier to quilt straight lines
It's best to start with your favorite casserole dish (or the one you're giving your friend for her shower). You want your carrier to be big enough to cover at least half an inch above the edges of the dish to minimize the chances that your 400 degree mac and cheese will slosh over the edges onto your lap, car upholstery or toddler. Measure the bottom and sides of your casserole, then cut rectangles out of your fashion fabric and lining, adding 1/2" for overhang on each side and 1/2" for seam allowance/ good measure because quilted fabric shrinks a little bit. (Note: I use 1/2" seam allowance instead of 5/8" for home sewing projects mostly out of laziness, but also because they generally need less fitting wiggle-room. 5/8" gives more room for fitting garments, but for something like this just add whatever seam allowance you like.)
After you cut your fabric, cut a rectangle of quilt batting 1/2" bigger on all sides than your fabric. You want some overhang because some of the batting tends to get sucked up during the quilting process.
Make a "sandwich" with your lining, face down, then the batting, then your fashion fabric, face up. Safety pin your sandwich together every 2" or so to keep it from shifting as you sew (this is called basting in quilting lingo. You can also do "real" basting with a needle and thread if you want: sew large running stitches about an inch or two apart in a grid over your entire "sandwich". You want these to be tight enough to hold the layers together, but loose enough to be able to pull out after you quilt the layers together with a minimum of hair-pulling. You could also use spray adhesive to hold the layers together. Here's a good YouTube video that explains basting: http://www.youtube.com/watch?v=MSeWBOnbC90 ). You'll have to remove the pins as you stitch if you choose that route, but don't skip basting one way or another or you'll end up with ugly puckers in your fashion fabric or lining.
Now it's time to decide what quilting design you're going to use. For this carrier, I just quilted diagonal lines about 2" apart
Ok, all quilted? The hard part (such as it was) is over!
Now it's time to lay out our ribbons for the corners. I used half inch grosgrain ribbon because it holds its shape better than satin ribbon, but whatever you want to use should be fine. Cut eight lengths of ribbon about 10" long (you can trim it shorter if you want after you've finished the carrier), and lay them out about 2 1/2" in from each side of the corners. You want them to meet up over the corners of the dish, so you could set your casserole dish on your quilted rectangle and fold the corners in to see exactly where the ribbons should be placed. Pin or hand stitch the ribbon in place on the lining side, matching raw edges.
(Note that the diagrams aren't to scale at all - they're just meant to show placement. I forgot to shade the rectangles in the diagrams to show lining versus fashion fabric, and I'm writing this as quickly as I can before my kiddo wakes up, so I'm not going back to fix the diagrams right now. Read carefully to see which side is which and feel free to ask questions in the comments if you need clarification!)
After your ribbons are in the right place, it's time to finish the edges of your carrier. First, using a ruler (I like the wide, clear plastic quilting rulers, but any straight-edge will work), square up your corners and trim off any extra batting that is sticking out and any threads still hanging from your quilting lines. Unfold your bias tape and line up the raw (inside) edge right-sides together with the lining fabric, leaving a 2" tail hanging where you started pinning. Continuing to unfold the bias as you go along, pin it around the entire rectangle, again leaving a 2" tail when you get all the way around. Stitch just inside the fold of the bias tape starting with your first pin (leaving the tail hanging for now) and stop at your last pin. Backstitch, then take your two tails and match them right sides together, marking where they meet. Stitch them together at your mark, trimming the excess to a 1/4" seam and finger-pressing the seam open. Then stitch the newly-attached bias trim the rest of the way to your quilted rectangle.
To finish the edge, fold the bias tape over itself, enclosing the raw edges of the rectangle between the halves of the tape. You have a couple of options here. You could top-stitch the bias tape, stitching through all layers about 1/8" inside the edge of the bias tape. It would look like this:
The trick with that approach is to make sure you're catching both sides of your bias tape and stitching in a nice, clean straight line. You can also fold over your bias a little farther on the backside so that you're "stitching in the ditch" on the inside (lining side) and catching the bias tape on the back (so the inside bias tape shows no stitching on it but the outside looks like the picture above). Or you can fold the bias tape to the outside as described above and slipstitch it by hand so that no stitching shows on the outside of the bias tape at all. (Here's a link to a very thorough description of hand stitches - the slip stitch is on page 7: http://www2.ca.uky.edu/hes/fcs/factshts/CT-MMB-002.pdf)
Finally, you need to decide where to place your handle loops. I made the handles with one continuous loop of webbing; the trick is just to make sure you place the straps across the bottom wide enough so that the casserole sits flat and is well-supported. If you imagine the smaller rectangle where your casserole bottom sits divided into thirds that should give you some idea of where to place your webbing, but you can always pin it where you think it should go, tie your corner ribbons and set the casserole into it to see if the handles are in the right spot before you sew the webbing on. It should look something like this:
After you decide how long you want the handles to be, stitch the ends of your webbing together. I cut both ends off cleanly and used a lighter to (carefully!) melt the end of the webbing and seal it so that it wouldn't unravel, but you could also use a close zigzag stitch to finish the ends, cutting off any fraying past the stitching. Next, stack the ends of the webbing and sew them so that you have a continuous circle. The inside of the circle will go against the fashion fabric so the webbing creates a sling that the casserole will sit in. Start with the ends of your webbing under where the casserole dish will sit and arrange the webbing as shown in the diagram above. You'll stitch a square with an X connecting the corners at each of the yellow Xs above to connect the webbing to the rectangle.
Finally, if you want, you can make a cushy wrap for the handles. Measure two rectangles of fashion fabric and one of batting about six inches wide and nine inches long. Sandwich them together, but this time put the fashion fabric right sides together with the batting on top. Stitch around the outside, leaving about three inches open on one side to turn everything right-side out. Once it's right-side out, tuck the remaining raw edges inside and edge-stitch around the rectangle. Stitch the female (soft side) of the velcro about two inches in on one side of the rectangle, then wrap that side around one of the handles and edge stitch, enclosing the handle. Your velcro should be flat against one side of your handle. Wrap the other handle in the rest of your rectangle and mark where your male (sticky side) velcro needs to go to meet up with the female. Stitch it on and you're done with your casserole carrier.
Make some delicious mac and cheese (recipe for my famous "book club" mac and cheese to follow), cover it with aluminum foil and proudly take it to your next potluck in your very own casserole carrier. My friend's mom carried the one I made around for the rest of her shower - it was definitely a hit. In fact, I'm not sure if my friend got to take it home or if her mom stole it. If you wanted to get fancy, you could even make a zippered or tied lid for the carrier to keep things toasty on the way to your potluck. If you make a carrier from this tutorial please send me a picture - I'd love to see what you come up with!