Fold it in half again so you have a square. Measure the distance from the corner with no raw edges to the top corner. This will be the radius of our circle. Mine was 55cm, half the width of my fabric. Then measure a few points from the corner with no raw edges. You then connect these points and end up with a curve. You can just make out the very faint curve on my fabric (sorry I should really have taken a better pic).
Cut along this curve and unfold.
You should now have a circle like this.
Lay this circle on top of a second piece of fabric and cut aroud it to give you a second circle.
Place right sides together and pin.
Sew around the circle, but make sure you stop 10cms or so before you reach the start of your stitching so you can turn it all in the right way.
clip seams. This is so when you do turn it in the right way the fabric sits flat.
Turn the fabric through the hole so the right sides are facing out.
You should now have something that looks like this.. You know need to sew up the hole, I topstitched the whole way round mine becasue I find it looks neater and helps the fabric to sit flat.
Now for the casing for the ties. I used pre made purchased at spotlight bias binding for this. If you choose to, you can make your own but I was running very low on time and only wanted plain old black. Here is a good tutorial for making your own. Just remember we want it flat, not folded in half. Mine took about 3 metres of binding.
pin your binding into place, only go half way around your circle, and then fold the ends over to finish the edge. Repeat for the second half.
Sew into place